I read that Satoshi never moved or spent his coins, so I expected to see his address stay unchanged since mined. But it looks like there are lots of small transactions: e.g. in the first address there are more than 1000 txs, and in the second address, there are about 65. What are those for? Who made them and why?
Of course, because Bitcoin is (mostly) anonymous, we can't know for sure who has been sending these, let alone their reasons. But some guesses:
People donating money to Satoshi, since it's known to be his address.
Mistakes. Satoshi's address is commonly used as an example in guides for creating transactions, etc, and it could be that some people copied the example and forgot to change the destination address.
Attention. I saw some transactions with attached OP_RETURN messages, e.g. this one (see under "Output Scripts" near the bottom). By sending to a well-known address, there is a better chance that curious people like you will stumble upon the transaction and read the message.
Just for lols.
There are altcoins and other protocols that rely on "burning" bitcoins by sending them to a well-known address with no known private key. A variant on this would be to send the coins to Satoshi. Either he eventually spends them (so it becomes a donation) or he doesn't (so it's a burn), but either way the parties involved probably aren't getting the coins back. I haven't seen this variant in practice but it's conceivable that someone has tried it.