However, once you throw (principally) dairy into the mix, including mass-market meat substitutes (such as Quorn which often contains dairy derivatives), your options expand to the point where it is easy to a) just drop the meat and increase veg. intake with supplemented dairy from common dishes or b) replace the meat with a price-competitive meat substitute.
If you did indeed mean vegetarianism in general then I’m keen to know why you think it is more expensive.
I’m with other commenters here that this is a weird cost-saving measure from WW, and that dietary choices should not be imposed on people like this (whilst acknowledging WW is a private company and can do whatever they want—- it’s just a strange way to force it on people IMO)
Also, I find that it's pretty easy to actually save money on vegan food. Maybe it takes a little planning, but it's not that difficult to walk away with more money eating vegan while feeling better.
I eat vegetarian 1-3 times a week and observe cost. I eat as much so that I don't feel hungry. If I am hungry I eat. Vegetarian days are more expensive.
Mostly because veg lunch itself is more expensive (or tiny) and don't last longer then 3.5 hours. Then I have to eat again, fruit and vegies are not enought (need nuts or dairy and a lot) or else my performance go a bit down.