I'd have to say this is probably pretty true, but I only use the words 'pretty true' for a big reason. The reason is the given which I'm going to propose, which is that people are using reputable wallets, which don't have access to their keys, and they ensure to save their paper backup somewhere. Now that that's out of the way, I would come to the same conclusion as OP because their aren't as many targets of hacks / malware / crypto coin stealing operations on mobile as their are on PC. But I must say that something like this will change if enough people are holding a shit ton of money on their phones instead of wallets on their computers.