Why is Lightning then not much more popular now, and L-BTC and Rootstock stay in niches? My interpretation is easy: the current on-chain cost is still low enough for people not being forced to use these layer2's. People don't do micropayments on Bitcoin (mainchain) since long ago anyway.
They will change when they have to but they accepted to use Bitcoin on chain and still don't feel to have big demand on layer 2 solutions. They can have better practice for transactions to save precious satoshis that will become more valuable with time.
The OP's concern is too far, 2140, probably we will all die on that year which is about 80 years from this year 2024. There will be many new upgrades on Bitcoin protocol and predict what will happen next 80 years is too far thinking. Like Segwit adoption, Taproot adoption, growth of Ordinals that happen only last 6 to 2 years lately.