Using a piece of software is not the same as using an online service.
If all those websites are using Flask, that would be the equivalent of centralising on Flask. The opposite of that would be many Flask-compatible yet unrelated other frameworks being used in parallel. A bug in Flask would not affect those not using that very codebase.
The centralisation people are speaking of here is the amount of people all putting their eggs in Cloudflare's basket.
> If all those websites are using Flask, that would be the equivalent of centralising on Flask
I agree on the equivalence between this and Cloudflare use, but not that this should be described as centralisation, which is a particularly potent word on the open web. Popularity isn't the same as centralisation. Each website could rewrite to remove Flask if they wanted.
Another example: if lots of people watch Squid Game, that doesn't indicate a centralisation of television programmes. No options are removed. People are just choosing to do a similar thing, but not in a way that centralises anything.
If all those websites are using Flask, that would be the equivalent of centralising on Flask. The opposite of that would be many Flask-compatible yet unrelated other frameworks being used in parallel. A bug in Flask would not affect those not using that very codebase.
The centralisation people are speaking of here is the amount of people all putting their eggs in Cloudflare's basket.