The problem is that even those "simple" things are a massive amount of work to get right (where "right" means bug-free, performant, well-documented (or intuitive - pick at least one), flexible, and with an ergonomic interface). Additionally, they're significantly more work than the even simpler restricted feature-set that the reMarkable currently offers.
I believe that the reMarkable developers are shooting for "quality over quantity" - polishing a small feature-set to a blinding shine, rather than trying to implement a larger feature-set poorly - that is, an intentional trade-off. I'm happy with that trade-off, but I know that others might not be - in which case, you'll probably get the Android device that other people in the thread are discussing.
Also, the reMarkable is open - you can add all these things yourself, if you're sufficiently motivated.
> something that I can pretty much get with a notebook
The reMarkable's features, as limited as they are, are still miles beyond what a notebook gives you. You have backup, synchronization, document export (PDF, raster, SVG), undo/redo, multiple documents, digital storage, cut/copy/paste, erasing (pen can't be erased, pencil usually leaves marks and has other problems), multiple brushes, page reordering, multiple page templates (lined, grid, music, blank canvas, and more), layers, really good handwriting recognition, and more.
Yes, it's light-years behind what we could have - but we're stuck in the place we're at because of a number of computing decisions that we made in the past (and continue to make now) that hamper creativity and flexibility, and overcoming those choices requires a lot of resources and the ability to ignore/bypass/counteract a massive amount of market inertia. The reMarkable team simply doesn't have those resources, so they have to make a trade-off - and the trade-off they made was quality over quantity (of features).