What is the biggest problem for crypto.

Biggest problem for cryptos is that nearly all altcoins are relatively worthless!

Bitcoin's blockchain is the only unique one to provide the most security in a decentralized, global, incentivized fashion.

All other "blockchains" are more closer to private worthless databases, my old nokia phone can do worthless databases. Other blockchains are simply scams. They need to be better than bitcoin on the below points but none of them are.

Bitcoin is ultimate store of value and its popularity has strengthened over time and maximizes value compared to any other altcoin...
Why are altcoins relatively worthless compared to bitcoin?:
If it wasn't secure, there would be no value.
If it wasn't immutable, there would be no value.
If it wasn't globally distributed, there would be no value.
If it wasn't resilient, open-source decentralized and unstoppable, there would be no value.
If it wasn't so scarce, there would be no value. If it was easy to spam transactions, there would be no value
If it wasn't minable there'd be no economic opportunity (game theoretic) cost and no backbone, there would be no value
If it can be shutdown, and have assets frozen by a bank or government, there would be no value
If it required a central 3rd party to function, there would be no value
If it was stopped after all major banks on Earth banned in 2013 to today, there would be no value. (say "bitcoin" when transacting and watch the block of the transaction. simple workaround=never mention "bitcoin").
If it didn't have the history of 8+ years (and still no hacker can exploit bitcoin blockchain), there would be no value
Bitcoin is on the verge of lightning network release rendering altcoins as only backup plan options if not dead. If it was exactly like fiat and only did transactions, there would be no value.

Bitcoin's value is worth well north of $100 billion USD today.

Bitcoin has all the characteristics needed combined to hold the most value and increasing more than any other financial-asset option coming from the manipulated fiat central-banking debt-system. (more than stocks, more than houses, more than gold).

If fiat/credit supply stopped growing, then house prices, stock prices, financial assets would crash significantly in value.

Governments and laws are controlled by the central banks. Bitcoin is an anti-establishment revolution that has already solidified itself worldwide.

Bitcoin cannot be controlled. It cannot be banned. It cannot be made illegal. And conversely it cannot be legalized. It just simply is. And people can always use it.
Popularity of Bitcoin will begin to explode with lightning in the next year.
Bitcoin's lightning network is emerging where fees will be tiny and cross-chain atomic swaps for decentralized exchange. For the patient, Bitcoin's price will be at the very least more than 4 times (400%) of todays price in 5 years.

Those trying to undermine and manipulate bitcoin stem from the central bank system around the world;
-the central banks dictate policy to all the operating big banks around the world and have essentially tried their best to ban bitcoin related transactions for more than four years straight, ever since 2013, and have failed at stopping bitcoin's growth, adoption, and popularity
-the central banks fund efforts to undermine bitcoin, providing plenty of capital and liquidity to private companies and venture backed groups such as Digital Currency Group (they own Coinbase, GDAX, Kraken, Bitpay, and media outlet Coindesk) and also Roger Ver/Bitmain to undermine and break the bitcoin protocol and/or manipulate trade

Above are just small examples.

First, educate yourself and then others. Please checkout the link to the bitcointalk post in my signature titled: How to teach Bitcoin to a 7 year old.

Bitcoin is a secure, decentralized, trustless and open system which cannot be banned nor controlled.

For global fiat (US Dollars, Indian Rupees, Chinese Yuan, etc), the fiat bubble system broke a couple of decades ago.

Fiat around the world is forced to inflate issuance as its heavily infested, burdened and broken with (the following whether good or bad):
-inflating fiat to keep house-prices from collapsing
-inflating fiat to keep stock market rising
-financing conflicts, bombs, missiles/aircraft/embassies, and "aid"
-frivolous legal costs (systemic resources wasted on legal threats, settlements, lawsuits bogging down system)
-regulatory burden on fiat banks & system (incredibly costly, lots of labor for each $1 in circulation)
-backstopping insurance frauds
-costs of auditors and budgetors and accountants checking the same thing over in governments and businesses (& still suspect)
-big insurance loss-events
-unemployment & other welfare costs
-stabilize regions after natural disasters
-keeping monopolies with internet access and information centralized and search engine crawlers centralized
-officially sponsored "money laundering"
-backstopping credit chargebacks
-state-sponsored corruption and unofficial corruption (governments and gangs, banks and conartists)
-retirement obligations (debasement in value to keep up with payments from government or other retirement-obligations)
-fake credit (goods being transacted with credit-loss, replaced by inflation of monetary base rather than bringing perpetrators & source to justice)
-using enforcement labor to freeze accounts and assets and take away your money

Bitcoin, systemically, is free from these limitations and burdens.