Here is a direct quote from 538:
538’s forecast is based on a combination of polls and campaign “fundamentals,” such as economic conditions, state partisanship and incumbency. It’s not meant to “call” a winner, but rather to give you a sense of how likely each candidate is to win. Check out our methodology to learn exactly how we calculate these probabilities.
In 2016 they gave Hillary Clinton a 71.4 % chance of winning, and in 2020 they gave Joe Biden 89 % chance of winning. They are dealing in odds, not calls.
And even if it isn’t getting through to you, how were they wrong in 2020?
What would accurate odds in the previous two presidential elections look like to you?