another dumb question: some blocks have say
Transactions ~2000
size ~1,600,000 bytes
Others have
Transactions ~800
but size is 2,000,000 bites
how less transaction have more size?
So, technically it’s random. Miners around the world are competing to find the next block, and the algorithm automatically gets harder or easier (adjusting every once in a while) depending on how much total hashing (mining) power is being put into it. On average, it balances out to every 10 minutes.
If you go to https://mempool.space you can see a visualization of this and scroll back through the blocks to see the time between them.
Discussion
I know it doesn’t seem like it, but there are lots of different types of possible transactions, some requiring more data than others, and you pay fees per byte.
Transactions can be anywhere from ~100 bytes up to 400 kB (technically they can go higher, but not without direct miner involvement).