often, hackers try to split the amounts into many wallets. so that later small amounts do not attract attention, or in this sense
There's no supporting evidence that those wallets got hacked. If that is true pretty sure there will be reports on forums/social media about "hey I lose my coin help" etc. This is just your assumption. Even if those are true, the reason is probably due to malware, bad wallet management, and other kinds of attacks, not some brute force gamble to get the private keys.