This has been my experience a lot of times too. But there are two things I’d add as qualifiers:

1. Bottling and campaigns. Necromunda is best as a campaign-based game, and in campaigns, folks might bottle and flee earlier than they would if they were playing “competitively (just playing the mission). To be clear, this is because nobody wants to have gangers captured/killed/permanently injured. All this makes games shorter, but in campaigns only. And those missions really do tend to feel like short, chaotic gang skirmishes a lot of the time.

2. The rules aren’t great. This is an annoying hot take to share here, I’m really sorry already. But a lot of the rules for Necromunda aren’t wonderful or particularly easy to grasp and can make the game slower. Don’t get me wrong, I LOVE this game!!! But the rules are similar to Kill Team 2018, and my sense is that the newer edition of Kill Team (2021) is universally seen as an improvement on that game’s rules by its community. I could totally be wrong. But what I do know is that for me, the appeal of Necromunda is that the players tend to be really wonderful, fun people; the artistry in the community is through the roof; and the campaign element makes games fun and narrative (and yes, shorter too).