Obviously ruby is bigger than just rails, but rails definitely popularized the idea of magical objects that are automatically syncing state and doing things on your behalf. This is presented by fans as surprising and delightful, rather than surprising and terrifying.
Popular python projects like requests and flask also lean into the idea of providing a programmer interface that is expressive but also maximally brief on the happy path—see especially the context local proxies in Flask (request, session); these look like global module imports, but they're actually request specific despite not being passed into your handlers... eek.
On the other side of things, languages like zig and go feel like a bit of a backlash to this, that no, magic is bad and everything should be explicit, even if it costs us a bit of code to do so.
Rust I think sits at an interesting place in this, because it's all pretty strict and explicit, but all the macro and type system stuff does re-open the door to offering some DSL-like things in a way that's perhaps a bit cleaner than what other languages would have to do to get to the same place programmer interface-wise.
Funny that you mentioned Flask, which literally started as an April Fool's joke [0], but that hasn't stopped it from becoming the 10th [1] or 11th [2] most popular web framework, with over double the number of devs compared to Rails, so "seriousness" likely has nothing to do with making people want to use it.
[0] https://lucumr.pocoo.org/2010/4/3/april-1st-post-mortem/
[1] https://www.statista.com/statistics/1124699/worldwide-develo...
[2] https://survey.stackoverflow.co/2025/technology#most-popular...