The problem with body armor is that it exacts a toll on the user. The more effective the armor, the harder it is for the wearer to adapt. Kevlar body armor weighs a lot and is far from breathable, so spending 8 hours wearing a 20lb vest can get quite tiring. Body armor capable of stopping rifle fire is oppressively heavy to wear, and a careful shooter can still exact a lethal injury by aiming for the head , groin,or armpit.
In the Trek verse of things, the situation is compounded because of the power requirements of an energy field. Making a nifty Stargate-type Goa'ould personal energy field means building a power source small enough to be portable, which would be tantamount to running around with a small power plant attached to your belt. I'd hate to be that guy if the power cell is damaged in battle -or if it overloads and goes boom!
Except that we have viable synthetic materials in real life that are much lighter and could serve as a substitute to 'heavy' Kevlar suits.
Furthermore, a piece of clothing doesn't have to be 'thick' in order to be warm.
Various metamaterials in real life and others can be used to create clothing that changes/adapts to the user body and 'breathes' but also provides ample protection against the elements.
The only reason we don't mass produce them is because of fictional notions of 'costs' (which have 0 to do with the actual resources or technical capability in doing something).
Since Humans in Trek have discarded money (and 'cost'), they simply create the uniform out of the best synthetic materials at their disposal with highest efficiency in mind (or at least, that's how they SHOULD be doing it - budget problems prevent this kind of thing actually being shown).
Granted, SF uniforms in that case would have been made to dissipate directed energy weapons (mostly) - but I would surmise that Trek writers (as dumb as they were) wanted to keep things simple (and as a result, completely shot Trek's technological credibility - not to mention social evolution - out of the airlock).