Quoted from Trekkie1978:

The better not force us to wear masks during the Wine & Dine and Marathon weekend races.
Wearing a mask on the bus ride to the corrals. I'm fine with it.
Wearing a mask while sitting in the corrals. That's fine too.
Wearing a mask while running? Forget it. Just not feasible. Look at the marathon this year, I was soaked by mile 3. By mile 6, I was completely drenched. People were falling over during the marathon...that's without a mask making it harder to breathe.
If you asked me, as of now, I can't see Disney going through with the Wine & Dine races. Those are at normal capacity. Marathon weekend is at greatly reduced capacity...Marathon/Goofy/Dopey do not sell out in minutes.

Quoted from Trekkie1978:

It wasn't the temperature as much as it was the humidity. When the race started, it was 95%. When I cross the finish line, it was at 92%.
And the full sun didn't help either...forecast called for clouds...they were out there, just not over Disney. Let me tell you, the cold Hershey Kisses at mile 23 were the best tasting candy ever!!!!
Did you make it through Blizzard Beach? I was a few minutes away from making the turn to head there, when they modified the course.
Did you do the 2019 Marathon? That one was a hot one too. 95% humidity at race start, but it quickly fell once the sun came up...it's just that it was full sun blasting us the whole time.