That is because Monero's difficulty adjustment algorithm takes several blocks to adjust with the network hashrate. iirc it takes 720 blocks for Monero to adjust the difficulty according to Network hashrate (it's not linear tho)
Difficulty in fact is dependent on Network hashrate. It depends on coin to coin and what difficulty adjustment algo they use.
This right here. You just took like four short sentences to say what I spent paragraphs trying to explain.