When I want to dig into a new genre, I first listen to the most basic/noteworthy examples of the umbrella genre (for example, I want to dig into electronic-based music, then I'll listen to the most popular albums based in the electronic-based genre that cover different genres within that umbrella genre, such as trip-hop, ambient and techno).
Once I've listened to the most popular ones, I listen to more albums within the vein of the ones I liked (for example, if I liked the album "Blue Lines" by Massive Attack, I'll try and find more albums within the trip-hop genre, if I liked the album "Selected Ambient Works 85-92" by Aphex Twin, I'll try to find more albums within the ambient genre, and so on).
This tends to help break down the big task of musical exploration and make it more easy to find particular music that suits your tastes.
Also, I find that genre classification can be immensely helpful, since if we were to just refer to jazz as just jazz, it'd be very hard to find albums for someone who likes a particular aspect of jazz that they might like (or someone who likes lounge jazz might even get recommended free jazz lol)
Of course, the only genre which is a huge umbrella term (and as such, probably lead to the joke about all these wide number of subgenres in music) is metal.
Like just take a look at them subgenres lad!
Also, many unknown artists don't want to label themselves as unknown genres, as this usually makes it a lot more complicated for them to be critically or commercially successful, and more often then not, if they choose to stick to unknown genres, they become niche musicians (take a look at vaporwave artists for examples of niche artists). Like, the most popular artists on internet music communities tend to be artists who take typical genres such as hip-hop and heavy metal and put a completely new take on it.
Usually when artists or groups become critically acclaimed or successful, they usually tend to explore other genres more often then not (for example, the Beatles or Radiohead).
However, in just regular music discussion with people, it's considered more "approachable" to list musical catch-all genres that more people might know more about, such as "Rock" or
Hip-Hop", rather then saying classifications that aren't exposed to the general public, such as "Post-Rock" or "Abstract Hip-Hop".
So all in all, if you're not really "experienced" with music, you most probably will find there may be an unnecessary amount of sub-genres all around, however, these sub-genres tend to help classify music in a way that helps you find more of what you're looking for.
Also, many times musicians tend to incorporate various genres into their music, making what they find appealing to them.