I also sometimes think, why the adoption rate was lower back in days because it was so difficult to use and keep the BTC in your wallets and on any exchanges (like MT GOX) but as of now many exchanges and Wallets have User friendly interface which every buddy understand easily and liked too.
No, it wasn't
so difficult to use,
Bitcoin Core is basically still the same as Bitcoin QT, it hasn't changed much in terms of
user friendlyness.
Sure, there's a lot more Wallets today and some of them might be more
user friendly than others,
but that doesn't mean it was
difficult to use in the early days, using it was always as easy as using email. Do you think email is difficult to use?
The
difficult part in bitcoin was never its usage, but to
understand it, what it is, how it works,..
to wrap your head around it, that's the hard part and that didn't change at all.
... mining them, this could have been eaisly done using a mobile device.
Mobile device? When did anyone actually use a mobile device to mine bitcoin?
As a proof-of-concept ....maybe, like that guy that mined with a pencil and a piece of paper.
In 2010 "mining" was just an optional setting within the Bitcoin QT wallet that you could activate.
If you did, your CPU mined blocks working in the background.
Some smart people tried (and succeeded) to optimize that process and wrote their own mining software, which was faster than Bitcoin QT.
If I remember correctly the first public GPU-mining-software came out around october 2010, GPUs were a LOT faster than CPUs so people started to use those.
Then in 2011 came FPGAs, not that much faster than GPUs but a lot more energy-efficient
and in 2013 the ASIC-era began.
I've never heard of
mobile mining devices,
every "app" that tricked people into "bitcoin mining" was a scam.