Former Clock NR Holder
Fantastic to hear that this event is on the way out.
1. The puzzle adds almost nothing new in terms of puzzle solving techniques, the only new 'skill' here is being able to manipulate the cube with your feet.
2. Not only is it difficult and time-consuming to run, it also requires a significant financial investment from delegates/organisers who want to hold the event (for a new set of timers, mats, gloves etc). In Australia, we have 5-6 cities with regular competitions, and transporting the 3x3WF equipment between those is also rather impractical. (hence, we've only ever held 3x3WF in one city)
3. It's unpopular. The delegate vote on feet and the decision to change the format to average of 5 (as they have done with previous events in the past) didn't do much to change the frequency at which it is held at competitions. Just over 2% of WCA competitors have ever competed in feet. Anecdotally, even some of the really fast feetsolvers think it's a joke, and some other cubers perhaps only participate in it for the sake of WCA profile completeness, and unofficial statistics like SoR, Kinch, Nemesizing, etc.
4. This one is just my opinion, but I think it looks quite unprofessional and has a negative effect on the image of speedcubing to the wider world. Whether or not we should care about this is another question, I think yes.
5. Also my opinion, there are already too many events in the WCA. At our 2-day Australian Nationals, we barely had time to fit in one FMC attempt, one MultiBLD attempt, and weren't able to host as many rounds of other events as we would have liked. Removing feet will free up time at competitions to host more popular events, or make schedules more relaxed which may have marginal effects on reducing scrambler/judge errors.
Sure, #1 also applies to one-handed solving and perhaps 7x7 solving, #2 and #3 apply to Clock and Big/MultiBLD, but I'm sure that the WCA delegates who voted on this matter over a year ago had more than just these criteria in mind. If 3x3WF did not currently exist, I very much doubt there would be anyone campaigning to add it to WCA competitions.