There are so many low values that either haven't appeared in any decent number yet or are as yet unknown and finds are still turning up every now and then so it's not really surprising.
Plus, people used them to play with, not to collect (the article below mentions how many collectors there were in the US although I expect they underestimated the numbers somewhat). The UK collector market is way smaller than the US too.

https://www.cigaraficionado.com/article/collectible-casino-chips-8118

Also, IF only used on French roulette then £10 then wasn't peanuts when the table was in play.
Luckily the odd chip does appear from house clearances and other such places so there is still hope.
Yes, some would have been destroyed but like Vegas, it didn't always happen that way hence the odd hoard turning up which is great.
As you say though, Torrey, maybe they also kept a close eye on them but they were always happy for people to walk off with the tokens as it made them a half decent profit.
Here's hoping that some more plaques (and jetons) appear on the market as they would be snapped up pretty quickly and given new homes.
There are still many chips that are only known notched too so we can always live in hope that un-notched one will turn up sometime.
As we all know, the fun is in the finding of new items that fill in the gaps and help us to figure out what was out there and used.