I think a lot more inhabitable planets will be discovered than we first expected.
At one stage some scientists even theorised that ours may be the only solar system, incorporating planets, in the universe.
I always considered that to be a poor quality theory and indeed many planets have since been discovered in nearby stars. Most of them are gas giants of course, purely due to their size and greater gravitational effects.
We don't know how many planets there are in nearby solar systems.
However 'inhabitable' depends on your definition.
Mars qualifies as an inhabitable planet, yet it is certainly a hostile environment.
If you mean a planet in the butter zone, with a proportionally suitable mix of breathable atmosphere for humans, sufficient field to deflect the sun's most harmful rays and a solid rocky base, then it may well be like looking for a needle in a space-like haystack.