This article explains it really well. The part about leap seconds especially got me. We literally have to smear time to keep servers from crashing. That’s kind of insane.
Everyone should use TAI as their fundamental representation. TAI has no leap seconds. It's way easier to convert from TAI to UTC than vice versa. You can still easily present all your timestamps in UTC when printed as a string.
NTP servers are generally synced up to GPS signals, which already use a version of TAI for their time signals. So an NTP server will take a perfectly good TAI time signal and do a smearing conversion to something that looks more like UTC (but isn't, because a true UTC clock would occasionally have a 61-second minute instead of smearing). Then someone never fails to freak out about the leap seconds because we have this oversimplified time abstraction that encourages you to ignore them. And instead of realizing they made a mistake in recommending UTC as the fundamental representation, BIPM is doubling down and is about to eliminate leap seconds entirely, so UTC will become just a worse version of TAI (because it will still have cause historical discontinuities with most software systems, but also drift away from solar time). I'm kinda pissed about it