It’s the only way to buy clothing sight unseen on the internet. If you don’t want to sell sized goods on the internet, don’t, but otherwise people need to try multiple sizes and return some.
A few years ago I needed a new pair, checked my size from my current pair, and ordered the exact same off Amazon. My old pair still fit, maybe even a tad big at the waist.
Then, perusing the catalog, I figured I'd also spice things up a bit, and ordered a 501 in a color I don't usually wear, for variety.
When I received them, the sizing was a complete joke.
It was absolutely impossible for me to put on the 511. My upper thighs would not fit inside the jeans without pulling on them, and after that it was impossible to button them.
The 501 was the opposite: much too big, could have probably went two sizes down.
I sent them both back, ordered a single 511 one size above, which was, you guessed, too big.
Frustrated, I sent them all back and went to my local brick and mortar store and ended up with a pair of 514s – one size below my regular one.
Specially with Silca being a cycling company, I think a lot of people here will be all too familiar with the phenomenon of "chicken legs" and how to find a pair of trousers to fit them into :-)
I'm not really built like a cyclist, so I usually have the opposite problem when buying cycling shorts :)
Although, to the point of this thread, I've found that actual sporting goods brands (as opposed to "lifestyle" or "sportswear", or whatever they're called) tend to stick to one set of measures.
I used to love my Gore biking shorts, so when I was in the market for a pair of running shorts, and saw Gore made those too, I ordered the same size and fit was the same.
I have similar experience with Decathlon, a French sports goods store, that also make their own products.
Ditto for Nike, where my basketball shoes are the same size as my running shoes – bought several years apart.
I would go one step further than just filtering. Production is usually still far too much manual labor (cheapest available). With significantly improved automation everything would change. Even just automating the cutting of cloth would allow to tailor to fit, not just standard sizes, with no significant increase in net effort.
Combined with sewing in cheap parts of the world and any kind of returns policy it becomes a logistics nightmare of course.
The solution is even higher automation.
I think you are seriously underestimating how big of a change in effort that would be. Just tracing and keeping track of a particular garment through the production would be a huge effort.
For a robot/computer.
Now what changes if you have an orderbook of 500 shirts all with custom sizes? You (or a robot or whoever) cuts out the pieces for order number 1. You can’t just grab any lefts and sew them to any backs. You need to sew that specific left with that specific back. After cutting do you mark the pieces? If so how do you remove the marks later? If not how do you QC that there were no mixups? After a shirt is done how do you make sure it ends up with the right customer?
These are all solveable of course. The thing I am disagreeing is that all you need is a robot to cut the pieces and then you can offer custom tailoring for little or no effort.
(And I'm not talking high-end clothes).
I only tried it once but it worked very well. Suggested a smaller size than I would have purchased and they fit perfectly.
Clothes are probably significantly more difficult than shoes though.
It's even worse. Some manufacturers have a single rough sizing table for an entire product category, like all shirts or pants. They will happily ignore different fittings and styles like slim fit, oversized, loose fit etc.
They sell a variety of high-end bicycle accessories including pumps, bottle cages, fancy lubricants (including chains pre-treated with hot wax lubricant). It's quality stuff with a pricetag to match.
A little research and review-reading goes a long way.