Probably the strangest question ever asked here?

Back story, I started fly fishing in March of 2020. I don't tie my own flies, but am wondering how long (roughly how many fish) a fly should last? I had one, early on that probably didn't make it through a limit of sandbass. I think it just wasn't tied as well as others. This past spring, on short notice, I had to pick up some clousers for a trip the next morning. I think I spent $30-40 and my first impression was "these must've been tied in one of their fly tying classes?" Literally, eyes spun around the hook.
Since the summer, I've bought flies in Colorado and here in Texas that have had thread hanging off of them a short time in. The latest, I went to cinch down a knot and everything from the eye of the hook back slid down the shank. This particular fly was commercially made by Umpqua. I bought 4 of these, thinking I'm sure to loose one and I will have an extra to share. I did, in fact, loose the first one! That was a learning moment. I'm down to one, I think, that is still like new. Total of no more than 2 hours of fishing time. No time in the trees, that I recall and 3 fish.

T-Gill, I have tied my own for years and there are so many variables to how long they will last. Some designs will last a couple fish, some a couple dozen fish and others longer. I put in great effort to build mine to last.
The material used, construction, and the fish will determine the outcome. Unless the caster hangs a tree or rock or other snag.
Example: natural material vs synthetic, toothy vs non, aggressive vs sluggish fish, how material is secured to the hook ie glue vs no glue, wax vs no wax, effective whip finish vs half hitch.
Losing and destroying flies is part of the game, there is no definite timeline.

Your experience seems indicative of a lot of commercial products, to continually profit corners are cut.

You've described the reason many of us tie our own flies.

As mentioned, there is no real answer to how long a fly will last. I suspect that most flies end up in a tree long before they wear out. If you can buy in person, you can see that some flies are tied better than others. Sort through the bins and pick the best ones. I realize that this is not a!ways an option.

For Clousers, you can add a drop of super glue to the eyes to help extend the life of the eyes. Try to minimize the amount of glue that gets on the hair on the point side of the hook. You want that hair to move. One other comment, it doesn't matter how much glue is used, bouncing a Clouser off a rock while casting will cause the eyes to get loose.

You can also add a drop of glue to the heads of any fly you buy to reduce the risk of it coming apart.

Good luck!

I've noticed sometimes you get a bad batch of deer hair. Not sure if it is the dye, or if it is just old and dried out, but the hair can get brittle and just break off.

As for commercially produced flies, I've seen very high quality from the discount bulk providers, and then I've seen very poor quality from the high dollar fly shops. Not sure there is any way to tell until you get on the water.

Thanks for all the input! All falls in line with what I had assumed.

Get a tube of UV Knot sense and while on the water a little dab on the head of the fly will save the fly. it must be dry of course,

Synthetic materials tend to last longer. Clousers can certainly be done with synthetic material like craft fur or steve Farrar blend instead of deer hair.

I try to carry along some UV cure material like Loon or Solarez for on the water repairs. One thing that tends to go quickly for many patterns is any kind of palmered hackle. One thing to help stop that is a few reinforcing wraps of tying thread along the length of the hackle wraps.

Basically, a person needs to look at exactly what went wrong with the fly and then come up with some measures to fix the issue. Spinning dumbbells are a fixable problem.

Commercial ties are just normally people in a far away nation paid to crank out flies. Commercial in these cases does not mean better.

Some patterns are inherently more fragile.