For the sake of the discussion, let's assume that the 16 MB limit is a harmless one. How do we enforce it in a softfork way? Segwit was enforced in a clever way, by separating the witness data from the transaction data. AFAIK, it's impossible to achieve it in softfork, unless you've figured out of another way to restructure the transaction data.
I don't think a softfork can do this, but then again,
when the limit was lowered, it must have been a hardfork too. Except for back then there wasn't much controversy about it.
Are you sure about that?
Because
even serious bugs early on were fixed with a soft fork.
"Why shouldn't this be done in a hardfork way?". It's already history, called "Bitcoin Cash". There is no point in redoing the same thing.
That was 7 years ago, surrounded by loads of contoversy, and promoted by some people with their own agenda. I don't think it's right to use that failure to keep blocks the same size for eternity. I don't think
a proper change, coming from the Bitcoin Core devs, that actually improves Bitcoin's future will be rejected.
But this isn't ETH where Vitalik's team controls the network... SHA-256 miners are in charge of the BTC network, so good luck trying to convince them.