Is "forwent" used much?

I see "forgo" used quite a bit, and "forgone" is quite common too. I can't say I've ever seen or heard of "forwent" and in fact, I had to look it up to make sure it even was a word at all. Is it used much? Is there an alternative that is more common?

I suspect it's more common to say, for example, "I decided to forgo treatment" rather than "I forwent treatment." But why?

Apparently not. There are only four citations for it in the whole of the OED, the most recent being dated 1596. The reason for its being seldom used is the same reason why other words are seldom used: they serve no useful purpose.

I suspect it's more common to say, for example, "I decided to forgo treatment" rather than "I forwent treatment." But why?

I think there is a tendency to avoid using non-basic forms (also known as the other 'principal parts') of irregular verbs that are themselves uncommon in the present tense. I suspect this is so because people cannot remember the proper form or find it awkward. For example, the verb slay is used a lot (slaying, slays), but how often do you read slew?

As for your other question, people tend to cling fast to the original verbs in set phrases. "Forego the opportunity" is perhaps the most famous one for "forego", and you will find that Google yields 33 000 instances of the past tense "for(e)went the opportunity." So there is at least one usage of "for(e)went" that is alive and well.

"Forwent" isn't used much because so few people know the word. Here is a message using the word that I posted today on facebook:

I added a layer to my torso and used liners in my gloves but forwent the balaclava. I would have been more comfortable with it.