I'm currently developing a bitboard-based chess engine for fun and can generate around 5.5 million positions per second on perft tests. I ran the same tests on Stockfish, which can do around 130 million positions per second. What is it that makes Stockfish (and other engines) so much faster?
There are a number of reasons. The Main one is its aggressive Alpha Beta pruning and late move reductions.
To explain a bit further. AB Pruning is a search algorithm which basically cuts out the number of nodes in its search tree. How it works is it stops evaluating when it determines and proves the move to be worse than another examined moves.
Late move reduction is a slightly harder concept but it again searches the "tree" more efficiently. It does this by effectively diving down a "algorithmically" more probably tree.
If I remember the release paper correctly the elo for Stockfish 14 is 3350 +/-5% and that was based off a 4 threaded CPU.
In short there are the implementation of mathematically proven formulae to do with pruning infinite possibilities to the most correct, whilst also searching deeper down the most probably correct line.