This is very true. Men's pants are tagged with their waist size and will also normally have their leg length on the tag. I've got a fairly big belly so I have a large waist size compared to my height so this is useful.
Having to do the mental mathematics to consider which size I am or having to try on the clothes to get an understanding would be a major pain.
I went to get a couple of pairs of jeans from a Plato's closet recently. I tried 6 pairs of different brand jeans, all 34/32. 4 pairs didn't clear my thighs, 1 couldn't button, the last fit. The cut of the jeans makes those numbers mean very different things..
I once bought 2 of exactly the same pants at the same time, after having the same one from a year earlier and liking it that much. They were both different to my original one and different to each other. I had to send the too tight one back and the replacement was different yet again. Seems like people just do not care enough that there is next to no standard.
My only charitable theory is that vendors order clothing in batches with only a general description being passed between batch runs. No CAD drawlings in the whole industry.
But all of my 3 pants must have been from the same batch but still deviated more than 1 inch in waist size to the previous specimen. So one was too small to wear, the other needing a belt.
They also cut the fabric multiple layers high with a giant stamping tool. The more layers of fabric they cut at once the more variance there is between top layer and bottom layer but the cheaper the process is. Higher quality cheap brands will advertise that they only cut x amount vs what the competitors cut so they have less variation.