It is because little endian-ness in speech allowed market makers to trade faster. If you have a commodity that's trading at around 24 or 25, there's no point in waiting to hear about the 20, you just care about the 4 or the 5. This allowed the HFTs of the old world to trade super fast and the rest of society adopted it as a result.
Just kidding.
Number systems in different languages get pretty weird. I still have people asking my why in Danish, 50 (halvtreds), 70 (halvfjerds), and 90 (halvfems) seem to have the word "half" in them, and it's half of 60 (tres) or 80 (firs) but not 100. The reason is the number system in the top half of the hundreds actually counts in 20s (snes) but that old word is basically never used anymore. So 70 is half a 20 to having four 20s, which got shortened (fire snes -> firs). Similarly 90 is half of a snes towards 5 20s, which we prefer to call a hundred.
There is some hope though. Swedish and Norwegian are reformed, despite also being closely related to German.
I did read a popsci piece about the effect on numbers on kids learning times tables. Chinese numbering seems much more sensible. 15 is just ten-five, 52 is just five-ten-two (Vietnamese as well). In that way perhaps it directly encodes the place value system that kids need to learn, whereas naming it "two and half of the score on the way to the third" is just confusing. Personally I sometimes do times tables in Cantonese, it seems to recall a lot faster than doing it in English and certainly Danish. If you think about it, the ten in the middle is just a constant, so you are only remembering two sounds. Also there's no converting between the tens version of the number (fifty) and five. The whole table is just combinations of the basic 1-9, with nothing in the units if it's divisible by 10.
The Danish case (at least for 50) was explained by Tom Scott in a numberphile video, I believe. https://youtu.be/l4bmZ1gRqCc starting around the two minute mark.
The half in the Danish 50 is derived from an abbreviation of an abbreviation, originating from "half away from three, times twenty" ((3-½)20 = 2½20 = 50) using some nice, outdated numbering orders. He doesn't talk about 70 and 90, but your explanation makes sense. That would mean there are two ways the "half" made it into the names for tens!
Just kidding.
Number systems in different languages get pretty weird. I still have people asking my why in Danish, 50 (halvtreds), 70 (halvfjerds), and 90 (halvfems) seem to have the word "half" in them, and it's half of 60 (tres) or 80 (firs) but not 100. The reason is the number system in the top half of the hundreds actually counts in 20s (snes) but that old word is basically never used anymore. So 70 is half a 20 to having four 20s, which got shortened (fire snes -> firs). Similarly 90 is half of a snes towards 5 20s, which we prefer to call a hundred.
There is some hope though. Swedish and Norwegian are reformed, despite also being closely related to German.
I did read a popsci piece about the effect on numbers on kids learning times tables. Chinese numbering seems much more sensible. 15 is just ten-five, 52 is just five-ten-two (Vietnamese as well). In that way perhaps it directly encodes the place value system that kids need to learn, whereas naming it "two and half of the score on the way to the third" is just confusing. Personally I sometimes do times tables in Cantonese, it seems to recall a lot faster than doing it in English and certainly Danish. If you think about it, the ten in the middle is just a constant, so you are only remembering two sounds. Also there's no converting between the tens version of the number (fifty) and five. The whole table is just combinations of the basic 1-9, with nothing in the units if it's divisible by 10.