Again with pants sizes

Remember when I was all excited about the size 12 pants I picked up at H&M?  I've worn them a couple of times now and they're a great pair of summer pants - light and cotton and super comfy.  The catch?

Please excuse my pale, hasn't-seen-the-sun-in-10-years abdomen.

They don't fit anymore!  They're too big!  And it's not like I've lost gobs of weight or anything, but I guess I've lost enough since I bought them that they don't fit. 

Of course I'm excited about this - I rather like shrinking out of clothes.  But I can't help but feel frustrated that these particular size 12 pants are too big, while many other size 14 pants I own and other I try on in stores are still fitting (or are even a bit tight), while most other size 12 pants (including H&M pants) don't even come close to making it over my hips.

Honestly, I'm jealous of men and their pants sizing: waist sizes.  Why can't women's pants be like that?  Most jeans are and that seems to work out just fine.  So why is it that any non-denim pants have to be sized starting at 0 and going up by two? 

I just don't get it. 

(Although now I'm tempted to try to find these pants again and try on a size 10, if only for the ego boost!)