Why should 180 days be to have checkpoints? You hardly can call entering the country a checkpoint, allthough it is allowed for IO to check.
When they wanted that they would have used the same system as marriage, elite and retirement, so why did they "invent" something new then?
But I just tried to answer your question why immigration is acting the way they do.
I am aware there is a way you can use DTV to live in Thailand year around, but Immigration does not see it that way, just like the majority does not see it that way, otherwise Google AI would also present it that way.
In daily live when are talking about leaving and coming back they mean they go somewhere else and stay there until they return for another stay. The useless trip to the border and back, only to get another 180 days is completely legal, but cannot be seen as normal use.
You seem to be focussed on border runs somehow, but the official does not mention that.
When you ask Google AI for "visa live in Thailand" or "visa expat Thailand" you will see that DTV is not one of the options, so obviously it is not my personal interpretation that DTV is not meant to live in Thailand.
He does not say so, you want to interpret his "other words" in that way.
Limiting it to 180 days a calender year might be a possibility, some countries do this, but it gives a lot of restrictions for people using the visa in the way it was meant, such as not usable for any course or treatment longer than 180 days.