To my knowledge gerrymandering only affects district races, e.g. state legislature and congressional house races. I don’t see a way a party can gerrymander a statewide race. It looks like what killed this was low turn out among Democrats.

You can’t win if you don’t vote.

“Democratic turnout has been weak” Louisiana- based pollster John Couvillon told The Hill earlier this week.

…

Cliff Albright, co-founder of Black Voters Matter, criticized members of the Democratic Party for not putting more resources into the race.

“There’s really no discussion, and more importantly, very little lack of investment in voter mobilization”’ Albright told The Hill. “That includes the party itself not putting a lot into this election, which, unfortunately, is a pattern that we’re seeing in Southern states in general and particularly in states that have Black candidates.”

quotes source