Like what standards, exactly? POSIX in its tabs(1) [0] and expand(1) [1] clearly states that tab stops can be wherever, and "every 8 columns" is just a default.
That still wouldn't give consensus on how many spaces people using spaces should use, it would (originally) give consensus on how many spaces a tab was supposed to be.
The few applications that don't let you configure it are less relevant now, and the alternative to consider tabs of varying lentgh would be to introduce a new spacing character in their place; hardly feasible.
[0] https://pubs.opengroup.org/onlinepubs/9799919799/utilities/t...
[1] https://pubs.opengroup.org/onlinepubs/9799919799/utilities/e...