There is still a big difference between attending a talk in person and watching it on screen. From AV issues (can you see their laser pointer) to the option of easily asking a question afterwards. Plus, many scientific conferences have poster sessions which are rarely accessible remotely.

And don't underestimate how important meeting new people and networking is! I would say that's probably my biggest motivation for going to conferences these days.

Isn't that the idea behind (academic) conferences? Bringing together everyone in a field to meet new people/network, and also learn from talks and poster sessions is the motivation. There is something I've found fundamentally different in being able to spend time with professors or graduate students "trapped" at a conference poster session than reaching out across time zones via an email->potential phone call. The ability to see tons of different research, ask stupid questions, and bounce ideas off of people in real time without any other distractions means that, to me, they usually are much more productive than I expected them to be.

I can immerse myself more in presentations when I'm physically there. YT is not the same. I can also grab the speaker and ask them some questions.

Also going to some new interesting places.

I don't know about other fields, but theorems often get proved at math conferences.

Essentially a vacation to a new destination paid by grant money. And the hotel bar soap.

Hotel bar soap.