It's a powdery mildew disease that's killing Impatiens Wallerana all over the country.http://msue.anr.msu.edu/news/impatiens_downy_mildew_a_curse_and_opportunity_for_your_garden

I first got downy mildew in 2014. I have large areas where Impatiens self-sow in large numbers. In 2014 they were completely wiped out along with my few potted impatiens. In 2015 they were back and did great. I suppose the seeds remain viable in the ground for at least 2 years because in 2014 I had no blooms to produce seed for the following year.
In 2016 they were wiped out again same as 2014. Last year, 2017, they came back even better than ever.
This year they appear to be doing well, so far. They just started coming up in the last few days about 2-3 weeks later than usual due to our unusually cold winter and spring here in TN.
The pics are from last year.

I haven't grown impatiens since 2013. As far as I know, they haven't figured out how to control the downy mildew disease. The spores are supposed to be active for many years in the affected area. I don't know why these plants are still being offered for sale.

Impatiens are still offered for sale because there are areas that have not been effected by downy mildew. I have grown them every year with success and so have others in my area. Even where it has appeared there are places that don't have it. Growers will provide seed and plants as long as people buy them. If they weren't selling they would not produce them so while you may have given up on them others haven't

All I can say is: mine are doing really well this year so far. I'll try to post some pics later. For me they perform as perennials. I love them. They self-sow everywhere and are never unwelcome where ever they decide to arise. It's like they decide to take over an area in my garden and I let them. Fingers crossed.

True jewels. I love them.