I have seen this complaint a lot but I think it is misplaced because it is frankly common sense to keep an update-to-date passport of the country you are a citizen of... People will have to apply for a passport and be done with it, nothing to see here...
Also, I suppose that the complaint comes only from people who live in countries that have visa-free travel to the UK and/or EU countries and who were just saving a little/money hassle otherwise they would already have an up-to-date British passport.
I'm a dual US/UK citizen, and the US has always required citizens to present their US passport to enter the US. The UK is doing the same. It's not a big ask.
Most years I don't visit the UK. My european passport is far more useful to me.
Note that this is an active change to the status quo. Up to and including today I had no need for my UK passport when entering the UK on my Swedish passport. From tomorrow I cannot do that and there's no reasonable explanation given for why this must change.
Edit: And while obviously this is not a big deal for me financially, there are a bunch of pensioners in the 3 million Brits living abroad and for many of them the £100 fee is a significant and unnecessary outlay.
Also, I suppose that the complaint comes only from people who live in countries that have visa-free travel to the UK and/or EU countries and who were just saving a little/money hassle otherwise they would already have an up-to-date British passport.