That's part of the answer, but the other part is that towing is going to reduce range significantly regardless of your fuel. With a gas or diesel vehicle that's not a big deal, because you can fill back up in 5 minutes or less. With an EV, it takes 20+, and the fast charging locations are less plentiful than gas stations. If you're not towing, that doesn't matter too much, but when you have to charge 2-3 times as often due to towing, it becomes a real issue.
Fast charger stations also rarely make allowances for cars with trailers. You often have to detach the trailer in order to get into the charging bay or park across multiple.
Not to mention you can't really charge while having a trailer.