When a person is ignorant about crypto, there's a high chance that he will stick to one coin alone but we should still consider the possibilities wherein a person chooses to stick on a single coin because he has too much faith and he speculated it well and proper. Not all the time we can laugh at someone that is not diversifying, we have our own reasons. You can diversify if you have observed that there's a high chance that many coins will shine or experience a bull run on the next few months but if not, there's nothing wrong on sticking on a single coin investment, specially with bitcoin.