The 1 MB blocksize was added to Bitcoin in 2010 as an anti spam "temporary" fix. Virtually every other coin has copied Bitcoin on this and inherited the problem.
That's half true. 1MB also serves as a sanity check to prevent blocks with sigops construed so as to require outrageous processing times.
That's why
BIP109 includes sigop and sighash limits, which are an unwelcome source of additional technical debt and magic-number-based cruft.
Bitcoin has a fixed emission with no tail-end after the main body of subsidies end, so it cannot use dynamic market-based Monero-style block sizing heuristics (unless we raise the 21e6 coin limit, which is simply out of the question).