Well the infrastructure is getting better on the one hand, but the main reason that people lost interest. Once the price crashed from $20K to $9K, a lot of people lost interest, cut their losses and sold off their coins, so there are fewer transactions right now. Let's see what will happen once the price starts rising again and reaches, say, the $15K level.
900 is really low, I was checking it two days ago and it was 6000. Still, I am afraid that your diagnosis (lost interest) is true and I can only hope that the cure didn't kill the patient. I hope, that is, that the interest is not lost permanently because people had been dissapointed in Bitcoin.
the number of Unconfirmed Transactions is a matter of perspective really.
as you may know every node has its own memory pool and each memory pool can have a very different minRelayTxFee settings. and thanks to that they can reject or accept different transactions. so for example when everyone was saying the number is 200k you could have found a mempool with 1000 tx.
also the number drops every time a block is found. and right now it is nearly 3000 Unconfirmed Transactions in the memory pool. 900 might have been the number that OP saw right after a block was found.
this has nothing to do with disappointment, price drop, ... it is simply thanks to spam attack stopping and some big services batching their payments to take up less space. additionally the price stability has reduced this number by only a little.