I heard it was poker-sites banning the (human) sharks

The biggest by far was american laws and regulations. the us uiega law in 2006 and “black friday” ie the doj raiding full tilt and pokerstars in 2011.

This decline was underway a full decade before bots really came on the scene.

The problem is specifically with unregulated sites that don't verify the identities of players. The bots aren't so much the problem as the fact that they can collude and share hole cards. But fyi, bots aren't actually good at playing poker outside of specific scenarios vs bad players or in scenarios where the decision tree is not large (ie short stack tournaments where the decisions are pre computed, you can imagine how massive your edge can be when you have a pair of 9s and you know there are already 3 dead aces and your decision is only all in or fold)

The decline of poker started when I woke up on Black Friday to FT, PS, and UB all having the DOJ logo on them.

I had to open a Canadian bank account to get my money out!

Yup, this was a much bigger deal than bots.