The difference, I'd argue, is that generally the loser of an election makes a public statement conceding that they lost. 2000 definitely was an outlier in this regard as well, but I think it still differed in that the disagreement was about counting the votes, not about the integrity of the election itself. Once you have a major candidate who's willing to make a baseless claim of fraud and a "stolen" election, suddenly the process that used to happen behind the scenes quietly in the past to count and verify the result that was announced earlier is put under a microscope and analyzed by people who have no idea how that process actually works, which is...well, almost everyone.
I might have been imprecise; in 2000, the claim was that the tallying of votes led to an incorrect result, whereas in 2020 the claim was that a massive number of illegal votes were cast and therefore caused the result to be different than it otherwise would have been. The former could easily be attributable to something like a spreadsheet error (like in TFA), whereas the latter would require malicious intent to commit election fraud. It doesn't seem surprising to me that alleging criminal intent to submit huge numbers of fraudulent ballots in what would have had to be several states would cause a larger public response and interest in the details of how votes are counted than arguing that a single state (Florida) should have to count the ballots again to verify the final total.
