what changed in bitcoin? how transactions are so cheap and fast?

Back in time i remember I had to wait quite a while for confirmation.

These days I send transaction with 1sat/vbyte without even looking at mempool, I get transaction confirmed in 15-1.5 hour max regardlesss of what fee estimators suggest.

And I had paid about $10 fee sometimes back in time. But these days, fee is 20 cent or less for any transaction.

What has changed?