At the moment, it is staffing rather than Covid-19 that is driving the restaurant availability shortage. Disney is hiring more and continuing to enroll college program but it is slow going. Epcot has the added wrinkle of no international CMs (which is due to Covid travel restrictions, in fairnesys to Disney).
Restaurants are opening up additional capacity but it is not across the board, it is one place at a time. For example, Oga's was fully booked for our trip and then suddenly tables came available every day, every time--clearly, they got the staffing they needed and upped capacity.
Also don't forget that people who are used to booking at 180 days, when most guests didn't even begin planning their vacations, had a much easier time. At 60 days, even before Covid, a lot of stuff was booked up. Now everyone is booking at 60 days and there is increased competition for reservations all at once.