It does drop more steeply, making it harder to hit, but it gives the opponent more time. Why not lower, just out of reach?
Both serves are valid options. There are a couple of downsides of the flick serve just over the receiver: Harder to play to the very back, serve is often a bit short or long. Harder to play with forehand (but relatively easy with backhand). If the serve goes too low and the receiver can intercept in midcourt, the rally is lost immediately. Can be weak if the receiver manages to anticipate it / stands farther back. Shuttle is easier to hit for the receiver, and comes back with more power, because it will be flying horizontally. The server has less time to orient themselves, shuttle comes back much quicker. At a beginner level, the very high serve is much easier to execute, and consistently brings the server to a very good position: when the receiver can just reach the midcourt from the very back (if even that), then the server just returns the shuttle to the front (or backcourt again) to win the rally. On the other extreme, in top-level Men's Singles, the receiver often stands close to the net and will happily smash down a slow high serve, so long serves are almost exclusively of the flatter flick variant.
when the shuttle drops straight down (from a high serve) it's harder to make a strong smash as some of the impact is absorbed by the feathers
Last one to add - because the higher the shuttle goes, the further back in the court the shuttle must be contacted. For a high deep serve, both of the opponent's feet should be outside of the court (definitely at least 1 foot out the back), whereas for a 'just out of reach' high serve, the shuttle could be contacted further forward, with both feet inside the court. The extra 0.5m might not seem much, but 1) it makes any smash less threatening because you get more time to react and 2) it makes any 3rd shot played to the front more threatening because they have further to run forward. The benefit of playing it 'just out of reach' is not great - they will still have enough time to neutralise the stroke in any case (they are unlikely to lose the point outright or play a weak return) which is the best case. Worst case, they predict you and make an effective attack. The deep, high serve is unlikely to result in anything but a neutral response (unless you are playing with someone capable of consistently jump smashing at 300kph+...i.e. elite level).
A theory, Generally for a high serve , if the opponent may have time anyway, eg not that far forward, then the very high one just makes it more awkward.
It may be just me but waiting under a high deep shuttle to fall back to my optimal reach also messes up my smash timing, I miss the sweet spot sometimes. So I purposely go to such serves a bit late.