I do wonder why they decided to have have separate shell size and pin designations given there appears to be a 1:1 correlation between shell sizes and pins (i.e. the 'B' shell is always 25 pins, the 'E' shell is always 9 pins). Perhaps there was plan to have fewer pins in the same shell at some point?
There's also 13-W3: DB shell, 13 pins, 3 of them coax: https://en.wikipedia.org/wiki/DB13W3. They were used for high-end workstation video back in the day.
And for reasons I don't fully understand, somewhat unrelated - if you look around almost any small business in my area, it's almost always VGA, rarely DVI, almost never HDMI or DisplayPort.
My theory is just that the cables came in the box and are screw-on when more modern connectors are friction fit, and the IT departments don't want the hassle of "they just got pulled out." Which should have been predictable - but I can literally see 12th gen Intel, paired with 1080p display, over VGA fairly regularly.
It's 100% because the VGA cable came in the box. Nothing about cables pulling because my lazy counterparts would not even screw in the DE15 cables half the time.
Source: Too many years experience in the desktop support trenches.
Confusingly enough, I’ve actually seen real, properly named DB-9 connectors. They were a cheaper version of a DB-25 to DE-9 converter. Instead of combining the extra pins properly, they just had a DE-9 on one end connected to only 9 pins on the DB end. They sometimes occasionally even worked properly at low enough line rates.
Coax and high-current/voltage pins are not that weird. You can also get truly weird semi-proprietary pins like fiber optics or even pneumatics/fluidics.
I use both DA-15 and DE-15 all the time in my line of work, and I am fastidious about using the correct terminology on all my drawings. Manufacturers are ironically some of the worst at getting this right.
You might be thinking of VGA connectors, which were a DE-15 connector, similar to a DE-9 serial cable, but with an extra row of pins and often pin 9 missing.
