It’s a loaded question, so let me modify it for you in such a way that it should partially answer itself:
“Why do the exoplanets WE FOUND have quick orbits”.
The answer to this proper question is that in 99.9% of cases we never actually see the exoplanet. The star has to be particularly close and the planet particularly big to get a shot at that (and even then only “technically”, as in we can get a spectrum of light passing through the atmosphere).
We see dimming or wobbling patterns of a star. And from those patterns, astrophysicists estimate the potential for it being an exoplanet and it’s likely properties.
But to determine whether there’s an actual pattern there, and not just random noise or a statistical fluke, you need a lot of data. And to get a lot of data, you need to be able to collect it in a reasonable time. And for a scientist, that means repeated transitions, as many as possible, within their observation timeframe, which usually isn’t that long.
So they observe a lot of fast orbits because that’s the one they can actually discern. It’s not impossible to at least attempt to measure the effect of a long orbit on a star, but it is particularly difficult. They just go undetected.