abs. abl. in Cicero

From Cicero’s Tusculan Diputations:

ferunt … ; raros esse quosdam, qui ceteris omnibus pro nihilo habitis rerum naturam studiose intuerentur.

Question: why not … qui cetera omnia pro nihilo habentes …

is it not a principle, that abl. abs. should only be used when more direct constructions are not feasible?

Not habetis (a verb) but habitis (a participle). “With all other things considered to be of no value”.

In fact, I think it is quite the opposite. Ablative Absolutes are only not used when they are not feasible. If an Ablative Absolute can be used, it often will.

This is how I teach composition. Any time you have a situation where one person or group of people are doing two separate things you have an opportunity to create an ablative absolute.

The soldiers attacked the city then burned it.
This is NOT an opportunity for an abl abs, since the soldiers are performing both their actions upon the same object. This would best be served by a participle.
milites urbem oppugnatam incenderunt.

The soldiers tore down the walls then pitched their camp.
This is perfect for an abl abs.
milites moenibus direptis castra posuerunt.

Latin will use an ablative absolute wherever it can, and participles the rest of the time. The last resort is a separate clause. At least this is my experience.
Your phrase ‘qui cetera omnia pro nihilo habentes’ is perfectly reasonable, but I suspect the abl abs was an upper class sort of thing, hence Cicy loves to get them in wherever possible.

Aha. Thanks.