What are omnis good for?
(1) Omnidirectional microphones can have full-strength response down to the lowest audible frequencies, while directional microphones ("cardioid" is one directional pattern from a whole range that exists, but it's the most commonly used) have less response below (usually about) 75 Hz or so.
Now, a lot of what's "down there" is often noise of various kinds, and the rooms you record in may have pretty crass acoustics at the lowest frequencies, but sometimes there is real music there, too, and in any case some people find it exciting just to have that energy there at all. It can be felt as much as it is heard. Very deep bass is one of the main things that initially sold the public on hifi back in the mid-20th century.
(2) The way you have to record stereo with a pair of omnidirectional microphones is either that you space them apart by some distance or else you put an acoustically opaque object between them. You don't really have the option of putting them close together (or even "coincident") and aiming them apart the way you can with directional microphones, since then the recording would be mono or nearly so (with both mikes picking up nearly identical signals).
As a result, the basic feel of a stereo recording is just different, because the whole way the stereo impression is created is different. And some people really go for the one way of doing it while others go for the other one, is all. If you're in this for pleasure, these are different pleasures that are available, and they're worth trying or at least knowing about.
--best regards