Do some people just paint with gloss paints? to avoid and save the step of the future floor/gloss cote step?

If not,why not?

I can't speak for everyone obviously but I think the general consensus is to paint with flats, then gloss coat with future or some product and go from there.

The reason for this, in my opinion, is that actual gloss paints are a) not usually available in the colors we need, and also b) are difficult to work with.

It is simply far easier to paint in the readily available flat colors that are also easier to work with. Follow up with a simple Future coat, which is self-leveling and as such is easier to work with than a gloss coat.

I do not worry about the gloss/flat of the paint I use on the base coat or any camo. I do use future on every tank before I put decals on and recoat the decals once they are dry. The future will let the decals go on with out silvering and protect the once recoated.
The biggest advantage to the future is it protects the base coat from all the nasty things I do with washes and oils and the like. If there was no future the thinners in the washes ect would soften and mess up the base coats or lift the decals. Years and years ago (pre-future) the best you could do was let a model dry for a week and use a non aggressive thinner and HOPE it did not lift the base coat. Now let the base sit for a day, shoot future, sit another day and weather away.