I think Slack really dropped the ball in 2020, and that's ultimately why the inferior Teams and Zoom platforms have been able to solidify their market shares, and Discord was able to bastardise some of Slack's old market share. It took Slack nearly 2 years after the pandemic started to introduce features like Huddles - by which point, everyone who needed video conferencing software (which was basically every white-collar worker in the world) had adopted one of its competitors. Now, even at companies where Slack is used, they'll also have a Teams account where video calls happen. This is the case, even though Slack had a video call feature hidden in their UI all the way back in 2019.
Although it's bad now, in Feb 2020 Teams was genuinely unusable hot garbage, chats didn't work, calls dropped often, files wouldn't attach to messages etc. Microsoft, for all their sins, recognised the imminent need for mass work-from-home tools relatively early, and made huge improvements to the platform before the end of March. By mid-April was in a usable state.
Slack's better software, but better software's not going to be adopted if it's missing or hiding huge key features.