Why are these daedra here? just wondering.

Wherabouts? I know there are some outside of... Tel Vos, I think. Maybe the proximity to the Telvanni is the reason?

Otherwise, it's probably just a gameplay mechanic for the creature spawn list.

There is daedras in most places in Vvardenfell.
And my guess would be game mechanics as well as they're near Daedric Shrines.

First of all, Telvanni often deal with Daedra. Aryon lets hostile daedra wander his tower and Gothren has Dremora bodyguards. The other consideration is the fact that they're far from Temple and Imperial influence, where both Daedra worshippers and "rogue" Telvanni can summon to their heart' content. And some probably escape their summoners' influence.

The DEVs just wanted to put some extra golden saint boob in.

Gameplay and story segregation, I'd say.

Wasn't there something written in MW about the Daedra being summoned and abandoned?

There's more of a history of Daedra worship/summoning in Morrowind than in most of the other Imperial provinces.

The explanations I can think of (take your pick).

#1 - Most of the ones around Telvanni regions are long-term summons or permanently bound servants of the Mage Lords, meant to protect ancestral tombs, personal property and artifacts from unworthy adversaries or travelers.

#2 - Perhaps these Daedra are holdovers from a time when the Good Daedra were worshiped. Having been summoned long ago in large numbers, many of them still exist to this day. Knowing now the rigors of age or disease they persist in remote areas.

There's lots of "wild" Daedra wandering around Azura's Coast and I think Molag Amur.