Honda, Renault, Porsche had all won championships before... Looking at long term, they can all be good bets. Short term, surely all 3 could falter.
The main reason is that RB's relationship with Renault has gone sour over the years so I think they're willing to dump Renault for whoever's reasonably good enough. I'm just surprised they think Honda's good enough now. TR has definitely demonstrated that they are not the slowest on the grid, but they're definitely not consistently fast. Anyway, I hope RB really has good engineering data to back up their decision.
If RB really won the title next year with Honda, McLaren folks probably would contemplate suicide.