How many regulatory bodies are there that need rules passed? I can think of the FAA, FTC, EPA, FDA, USDA, and the NRC just off the top of my head. A quick google search shows there are 19 of these rule making agencies. Even with a wide distribution of rule making authority, these agencies struggle to keep up with our rapidly evolving world.
Forcing congress to hear and make a decision on every single regulation these agencies propose would be a bottleneck that brings this country to it's knees.
Removing ~3 weeks vacation gets you down to 245. Eleven federal holidays? 234.
200 days/year sounds like an almost full-time job?
Also, most sessions only run a few hours, and many more are pro forms, where the minimum quorum show up (I think this is something like 15 or 20), open the session and then immediately close it.
Sure, Congress is in session for about 200 days, and even when it is the elected officials aren't typically on the floor for the full day. But that doesn't mean that when they aren't on the floor they aren't necessarily working. They could be meeting with constituents, with their staff, reading bills, going to committee meetings, just meeting with other reps/senators etc.
You make it sound like they don't do anything.
https://www.opensecrets.org/industries/indus.php?ind=E01
So due to the ignorance and corruption among conservative lawmakers regarding climate change and carbon emissions, congress has been in an ideological deadlock on the issue of climate initiatives. The EPA existing somewhat independent of that framework was a benefit.
Because then you're left with who is better convincing uninformed people; the experts, or paid lobbyists.
2. Politicians, per definition, are elected to represent the interests of their constituents. Many constituents disagree with experts (climate change, for example). QED, there is little motivation for politicians to listen or follow the advice of experts, especially if an expert's conclusion is not popular.
They can and should take advice but the whole point of democracy is that the policymakers are democratically accountable.