>>812354
Pretty much this. Japan has already perfected the process of turning manga to anime that there is hardly any need to take risks. Also, a lot of manga start as one-shots even before they become a series so they have less incentive to do a pilot, but pilots are still done.
You probably are not seeing a lot of pilots because they aren't listed as such. Probably under OVA or just a name on it's own. Just like any other medium, most studios would try to go for an already established series fanbase, and if it's popular, put out more anime for it if the first season does well. An original idea is hard to back unless you convince investors by showing your studios capability by keeping a schedule or just name recognition.
Little Witch Academia and Death Parade started out as pilots that turned into actual series later. They came out in a Government sponsored effort to raise new talent in animation while working under an existing anime studio. It's about 3 a year last I checked from what I've seen but those 2 are the most notable that come to mind.
There was that Japan Animators Expo with a bunch of new pilots I guess. They were more of a showcase than actually trying to be a series. The most recognizable things to come out of that are the mememe! music videos and Dragon Dentist which got 2 OVA parts for a movie.
Houkago no Pleiades (one of Gainax's most forgettable anime) started out as a bunch of shorts. I could be wrong but I was sure those original shorts were sponsored by Subaru, which happens to be the name of the character for the show. I know One Piece did eventually animate the old Romance Dawn one-shots, both of them I think. Shonen Jump I know does a lot of pilots that they showcase at their own con as a test run before the series starts, to showcase their voice actors. They aren't finely tuned in music or sfx but it's there to give you an idea of the animation and how the characters will sound like.