Only in Dark Avatar or the base game. The max amount of habitable planets has been drastically reduced in Twilight of the Arnor. From what I recall, this was done to reduce the memory usage and allow a bigger map size (Immense).

Still, you should have at least one habitable planet per star system. So, are you absolutely certain you've set the habitability to abundant, and not just the number of planets in general? It's a common mistake. Happens to all of us.

The data for the map generation (number of stars/planets/habitable planets, etc.) is hardcoded. Without access to the source code, it's not possible to change any of this.

@Gaunathor:

I`ve set both, planets and habitable planets, to abundant, but as I said, I have many star systems without any havitable planets. Often I discover systems with 4 or 5 planets, and each of them is an empty (on the strategic map) planet, class 0.

Interesting thing is, before the Community Patch I had many, many habitable planets with these settings, and nearly no star systems without any habitable planets, even if they were only low class. But now I have an abundance of worthless crappy planets. Another interesting thing is, that I don`t seem to have planets with a quality below 9 or 8. In the version without CP I had often planets with quality 6,5 or 4.

Weird thing that is!

I don't recall what I was playing - probably DA with the AT mod - but I was surprised to find a number of PQ1 worlds, with several PQ2 and PQ3.   Previously observed low was PQ4. 

Max, I just finished an all-Abundant game of TotA 2.20.  By eyeball estimate, 20% of the star systems have no habitable world.

How is your 'Extreme Planets'-setting in the galaxy-creation setup?

Extreme planets generally tend to have a higher PQ than normal habitable worlds.