And so they shouldn't! In many (most?) US states, the public schools are unconditionally funded by the state based on student enrollment figures. Cutting teacher pay during a closure under such a system would be a purely greedy move.
I don't know how it works in the majority of states but I know the model of mostly state funding based upon student enrollment is not universal. In my state the majority of funding is from local tax revenues. For example the budget for my local school district is approximately $1.3 billion. $370 million comes from the state and $30 million comes from the federal government. Another $40 million comes from "misc other sources" and $860 million comes from local tax revenue.
Sources: https://edsource.org/2019/californias-school-funding-flaws-m...
https://nces.ed.gov/programs/digest/d13/tables/dt13_203.20.a...
My wife taught K12 for 12 years and then became an instructional coach teaching teachers how to teach. There's a shitload of work if you want to do it right, and at least half (in our district anyway) will stretch themselves extremely thin to do so. Half of the rest are 9-5'ers and the remainder are shitheads.
Perceived equity issues fed into this as well. The result, of course, is that parents who have time to teach kids have kids who are learning, while the vast majority of the district is learning nothing. With remote learning, the results would be less differential. But I guess the districts feels worse about inequities it contributes to than ones that arise out of inaction. We have a 1:1 program, so all students have technology.
But I would the union preempted this, and is what made this discussion moot.