Serious issues with Warframe-mod-drops as soon as Warframe is 30?

[TachiFoxy]

I'm not sure if that's supposed to be like this, but I've had my Excalibur at level 30 for quite a while so far and, whenever I find any Warframe-mod for the past few days I've always only obtained "+XX% armor" mods. I wonder, what happened to the other kinds of mods, like shield-mods and the sorts?

I'm asking because I could imagine that a lot of people could get confused about the difference between "+XX shield" and +XX% armor" mods, equip themselves with armor-mods and they might sell shield-mods just to then be unable to ever get anything other than armor-mods. Unless, of course, they'd go and buy a new Warframe or build a new one to be able to obtain Warframe-mods below level 30 (and, as such, Warframe-mods that are anything other than armor)...

TL;DR: Why do only armor-mods drop commonly anymore the moment your Warframe is level 30? This can potentially be bad for people that sell other kinds of mods because they may never be able to regain any like those without leveling a new Warframe.

[nzzero]

I get armor mods almost all the time and im leveling a frame from lvl1. I dont even remember when was the last time ive gotten one that wasnt armor.