It's not that I mind the questions because I do anything illegal, but I don't like the level of private details they ask.
This is my situation for all things privacy related. I'm not shopping on darknet markets, I'm not buying or selling contraband, I'm not funding terrorists, I'm not stealing anything, etc., I just don't think private corporations, banks, or the government, have any business snooping on all my activities. Whatever happened to innocent until proven guilty? Mass surveillance, including the type of financial surveillance being undertaken by centralized exchanges and banks, does not make us safer or reduce crime. It is simply a method for the government to control the populace.
But since I'm straying off topic, I'll stop there since I could rant about this for days.
For instance, they asked how much crypto I own.
My honest answer would be "I'm not sure". I know where all my seed phrases are backed up and how to access all my wallets, but other than the couple of wallets I access daily or almost daily, I only know a ballpark figure of what's actually stored on most of them. Or perhaps you could say that you don't own any crypto - all you do have in your possession are a variety of hexadecimal/Base58 strings which may or may not be valuable.
Isn't that simply to ensure they get their money?
If it's for tax evasion, they won't care about a maximum amount either.
No reason they can't get their money via a bank wire or similar, even before they start the job if that's what they want. There are a plethora of reasons people will want to work for cash - anything from tax evasion, to avoid wages being garnished for loan repayments or alimony, continuing to claim unemployment benefits, illegal workers (immigrants, criminals, underage, etc.), and so on.