[amelius]

There is a simple solution: if companies do not respect do-not-track then why should we respect robots.txt?

[nostrademons]

Because then you end up in an arms race that the little guy usually does not win.

There are a significant number of crawlers out there that don't respect robots.txt. The usual response to them isn't to roll over dead, it's to get CloudFlare (on the technological end) and/or sic the lawyers on them (for CFAA, IP, or ToS violations).