In my area, it is almost always about getting paid.
Most units are not really above the ground by much, the brackets are installed well before final grade is done and the elevation usually finishes within 6" of the finished grade. Bear in mind that someone has to lift the condenser up there.
Yes, walkouts and other significant slopes will force a wall mount bracket.
Brackets cost more to buy than a plastic condenser pad- then you have to install them. Now, with enforcement of silica dust hazards, drilling into concrete without the proper safety equipment is a problem for cheap employers. It has always been a problem for the employee because most employers do not care, nor will they properly fit-test for a respirator.
More often than not, the storebought welded ones are not really square, or there are imperfections in the concrete that result in the wall bracket being out of plumb and/or "loose".
I have always used long galvanized wedge anchors with a nut to hold the anchor to the concrete, and then 2 more nuts to plumb the bracket. Takes more time and expense, and a tract home contractor will not do this. My brackets are plumb and tight.
A tract home contractor will use Tapcons or the new large spiral type anchors that sort of look like Tapcons, but aren't. Sleeve instead of wedge anchors will be used. The bracket will be anchored directly to the foundation, but some use a washer between the foundation and bracket to deal with concrete form imperfections.
The wall brackets can be installed pretty much as soon as the forms come off and the backfilling is done.
The pad can't be set until the grade is close enough to done, or to a point where a couple of bags of stone will finish it. But, if the grade settles a bit, then the contractor is coming back to re-level the condenser. And then losing what little profit there is in residential new construction work.
