What is the estimated fee and estimated weight of a block and why do they change so often?

What is it Estimated fee and estimated weight Why does it change so often in one block? https://mempool.space/api/v1/block/00000000000000000001c680ee86b8eaa43c94ac9012f4d2dcbfa9f45beadf06 Last time I checked "Estimated fee":27191335,"estimated weight":3991985