The issue is that whilst people want it there is never a good enough “reason” for that other than I want it, Maemo doesn’t give you more freedom than what AOSP does already at least not on the software level, you can degoogle and Android phone completely and do w/e you want with it. However people don’t seem to be doing that, and those who do often do that for academic purposes rather than to have their own personalized daily driver.
Even more so often the wishes of many people when it comes to customization doesn’t even require a rooted phone and a customized AOSP ROM, if you look at what people customize on their desktop which is often limited to their desktop environment and their workflow can be done on stock Android using alternative launchers and other apps.
Wanting for an Android competitor for the sake of having competition is fine, but it won’t look much different or it won’t be much of a competitor.
The other problem is that you have to choose between hardware quality and customization, because hardware is locked down and there isn't enough economic air left in the room for a third player to be able to invest enough to compete.
As for not looking much different from Android, the key difference would be where the control lies, and what the mindset is around control. You should have a robust code signing and containerization/permissions system, but those should be in the hands of users. With Android every single app installs with permission to portscan every network you connect it to. You will have an app store, but the user will come first, not the ad network.
App distribution was also better on both platforms. Maemo used apt under the hood, and Preware[1] was phenomenal. These days the two vendors that own 99.4% of the mobile OS market[2] don't want to let you install apps unless they can get a 30% cut.
[1] https://webos-internals.org/wiki/Application:Preware
[2] https://www.statista.com/statistics/266572/market-share-held...
They both allow free apps.
I liked my Nokia N900 and kept up for a while with attempts to keep its Maemo going after Nokia abandoned it. However, a decade later Maemo has bitrotted and its dev community has dwindled away. Nowadays the Phosh interface (i.e. the Librem phone, or Mobian running on the PinePhone) is seen as the most promising Free Software choice in the long term. Sailfish OS is also actively maintained, but its UI layer is closed source.