While I'm not a professional vehicle upfitter, I do a good bit of wiring. Low voltage, networking, and RF gear (LMR, WLAN, and soon some LTE).
Time: I'm of the opinion that this equipment should not be so prone to failure as to justify adding connectors inline. It's different if your vehicle is frequently changing, due to this being a hobby or demonstration vehicle. Connectors take time to install -- I can cut the wire and do a butt or lap splice faster than I can install a 4 pin connector.
Cost: Good connectors aren't that cheap.
Complexity: It introduces another point that may fail in your system. It also introduces connector loss, though that's not a concerning design criteria for these low current DC systems. In the auto industry, there's a phrase "stop comebacks". I don't want an issue to occur because of a faulty installation.
For these reasons, I do not.