Definitely file Trafalgar and Old Credit under the "how do they still exist?" category. Overall though I feel there's just so much middling, unremarkable beer in Ontario. Whether it's the trend chasers looking to capitalize on something popular, or the run-of-the-mill small town breweries catering to a captive market, I've had a lot of mediocre beers. Thing is, a lot aren't necessarily bad, but do little to make me want to buy them again. I'm sure it's the case with most markets though, but I've tried far more beers from Ontario for obvious reasons so it skews the average downwards.
I suppose there's still a large majority of drinkers who've moved to craft, but still prefer very safe styles or just don't care about the beer as much as the ambiance/community aspect of local breweries. It's tricky to list the worst because with a few exceptions, even my least favoured breweries make rather enjoyable beers from time to time.
The constant need for new, boundary pushing flavours for the trend chasing ticker crowds has changed the dynamic a bit now too. Breweries that I love have put out some of the most vile (to me, I know, subjectivity) beers I've ever had because of this seeming one-upmanship of extreme flavour combinations. Hence why it's again tricky, because with exception of a few categorically and objectively bad breweries, I've had beers I loathe to beers I love from almost every place I've tried. There are also a few where I've only had a couple beers, so it'd be unfair to make a sweeping judgement until I try more- the Golden Ale from Norse Brewery I tried a while back was truly awful, but it's all I've had from them.
That said, I could easily list a number of my least favourite beers from Ontario.