Everyone getting an A isn’t reinforcement. Reinforcement has to be conditional on something. If you give everyone who writes a long paper an A, that’s reinforcing writing long papers. If you give everyone who writes a well-written paper an A, that’s reinforcing well-written papers (and probably more what you want to do).
But if you just give everyone an A, that may be positive, but it simply isn’t reinforcement.
Everyone getting an A isn’t reinforcement. Reinforcement has to be conditional on something. If you give everyone who writes a long paper an A, that’s reinforcing writing long papers. If you give everyone who writes a well-written paper an A, that’s reinforcing well-written papers (and probably more what you want to do).
But if you just give everyone an A, that may be positive, but it simply isn’t reinforcement.