Many barrel racers are actually small people and teens who are not adult sized yet, need the smaller seat sizes. Add in barrel racing is a speed event, so weight can count when runs come down to hundredths of a second. Larger sized ladies do compete, but there are less of them, so they have less bigger sized tack to sell if they change saddles.
I personally do not care for barrel saddles because they are more specialty built with the higher cantle to aid holding riders in place during starts and running patterns. For me, the higher cantle “holds me too much” in place. I cannot move around much when using the saddle for any other horse activity like trail riding, pleasure ring work. I also think with the high cantle, rider probably needs to add an inch to their usual seat size, to be comfortable seated so upright. More work lifting right leg higher to clear the high cantle each and EVERY time you mount or dismount. Easier to snag your leg if not paying attention to getting leg up and clear, to get seated or dismount.
Roper saddles are made for easier on and off with lower cantle clearance. Seats come in more sizes to suit men and women. Horn styles vary, you need to find what you like, that doesn’t get hooked on clothing during mounting or rides. Pleasure type saddles can use various things from all the specialized models.
It can be hard to find a saddle that fits you well and fits the horses you ride. I am firm in picking saddles that let my body be aligned, head, hips, heels, so I stay comfortable at the end of my ride. Not all saddles let you ride aligned! I do not think a saddle MUST be custom made or cost a thousand dollars. There are lots of very nice used, less expensive saddles in 15-16 inch seats out there.
Do always ask if seller is measuring seat size from just below the horn, back to the cantle stitching or back of the seat where your rear touches. Going to the stitching can add a half inch! That is a half inch you cannot actually sit in!! “Experts” seem to measure seats both ways, so asking is important.
My saddle fixer hates the lightweight saddles with plastic trees. Says they do not hold up well in heavy use, not worth replacing. This is even good brand names. So be wary of those types.
Good luck finding something nice.