The first week of May is a little early in that zone, which is probably why it took them awhile to get going.
I have quite a few plants still producing like crazy including Green Zebra, Sungold, White Wonder, Early Girl, White Wonder, Yellow Brandywine and Paul Robeson (which seems to be slowing down now.) My Yellow Brandywine and White Wonder were very slow to produce and are just now really productive.
I assume they've taken on a "now or never" mentality haha

I was wondering if it's the "now or never" mentality too.

Agree with shady....Maybe, when they cannot grow the fruits any bigger or more, concentrate on ripening, to accomplish their mission. Even then the window of opportunity can be short.
My lone brandywine had just 5 or 6 fruits and could not ripen any of those. Black Krim almost finished the job. So did most of cherry types.

I am a full month or more behind schedule this year, and I have a counter top full of ripening tomatoes. What is surprising me is that the taste is still good. But these are 1 pound plus tomatoes, some of them, that just stopped progressing for the longest time. It is very welcome, just very unusual for this late. If we weren't having a late frost his year I may not have gotten many at all. Even now, not enought to do any canning. Not enough ripe at one time. For me I think it was just the weather this year.

My Sweet 100's went nuts.

If I plant early seedlings and weather still cold they just going to sit and wait... my experience using WOW is best if you have chance or floating row covers, temporary cold frame etc. Just planting out early does nothing to improve timing, although there are some varieties that will have better fruit set during cool weather.
Chicago weather can have cool summer or hot summer so this is one reason why I plant many different varieties, there will be something that works best for whatever weather we are going to have.