Made-to-measure mail-order dress shirts are an idea from the 1990s AFAIK. A while back I collected some promotional offers from in-flight magazines and online and ordered a big stockpile of white made-to-measure dress shirts. With the promotional pricing it came out to less than $20 a shirt.
As with any menswear business, the main problem is customer education. Men in the US dress like slobs, do not care that they dress like slobs, and do not want to spend money on clothes (85% of apparel revenue comes from womenswear).
I would rather not dress like a slob, but barring me finding a place to make me something that actually fits (for a good price).. everything I buy will fit somewhat awkwardly, and make me look as if I'm wearing several flower sacks sewn together or somewhat awkwardly in fit in other ways.
http://www.mv-voice.com/news/2014/09/02/a-stitch-in-time-at-...
https://www.google.com/amp/s/sacbee.relaymedia.com/amp/news/...
http://sandiego.communityguides.com/content_mobile.php?pid=4...
You could easily conclude from this list that it's rich peoples kids creating solutions to imaginary problems - "Oh, how could my poor feet possibly survive the arduous journey from my front door to the uber in an off the shelf pair of shoes? I need a tailor!".
I think we should give them the benefit of the doubt though since these companies are presumably a small subset of those they've invested in.
A more charitable explanation might be that since these companies are in SV then it makes sense for them to start out selling stuff to affluent customers who are not overly price sensitive.