I don't understand why there aren't planets with earth like atmospheres but many other games achieve this no issues, Empyrion and NMS to name a couple.
It all depends what shortcuts you can get away with taking.
I like NMS' planets and they're good fun to explore because there's a lot more variety of things to find than on most ED worlds, but in terms of portraying ELW-like environments they take a lot of shortcuts [1].
1) Single static water level. Below that level is wet, above that level is dry, there's a little bit of cosmetics on the borderline to simulate waves, but no rivers/mountain lakes/currents/tides/etc. Rainfall doesn't leave surface water except very briefly cosmetically.
2) Single planet-wide weather. If it's clear, it's clear planet-wide. If it's stormy, it's stormy planet-wide. If it's weird anomalous stuff, it's the same weird anomalous stuff across the entire planet too.
3) Single terrain type (hills of various sizes)
The problem with portraying an ELW isn't the graphical display of a thicker atmosphere - Frontier could turn up the refraction index and add some cloud-style high-level fog to the existing low-pressure worlds pretty easily. The problem is all the
other differences between a tenuous world and a thick-atmosphere world: Elite 2 technically had ELW landings back in 1992, but in terms of what you could actually
do there was no difference between an ELW and a no-atmosphere rock other than the ELW settlements having Odyssey-style open air landing pads.
If we do get further "landable" planets my guess is that the next ones will be gas giants and the ultra-high-pressure rocky worlds where your ship would be crushed long before reaching the actual surface: the atmosphere is dense and there's a lot of scope for spaceships, floating stations, floating space jellyfish, etc that aren't really possible in the existing environments, but the atmosphere's interaction with terrain doesn't need to be considered and so the weather systems might vary planet-wide but are relatively simple and can be long-term stable (e.g. Jupiter's red spot and bands, or even Earth's upper-atmosphere stable convection cells)
[1] Every game portraying any part of an ELW necessarily takes a lot of shortcuts; for your typical "set on Earth FPS" the shortcut is "don't map more than a few square kilometres of it", for example; for Civilisation the shortcut is "extremely low-res abstracted map". This isn't a criticism of those games. The problem is that the shortcuts other games take wouldn't really be compatible with Elite Dangerous: a single planet-wide weather condition is fine in NMS (you have to pay a fair bit of attention to notice that's how it's done) but has big problems in ED because of the much higher multiplayer persistence and the aim to be portraying 80s Serious Military Scifi rather than 60s Pulp Scifi ; restricting people to not leaving the spaceport is fine for a lot of games but again not for ED, etc.