1.) VMware had (and still has) a lot of goodies on vSphere that were (and some still) are not on competing products. If your Virtualization strategy depended on any of these, migrating is hard.
2.) Take point #1 and multiply by 20x if you have (private/public/hybrid) cloud foundation.
3.) If you were a single-virtualization or single-(private)cloud vendor based shop, you probably want to migrate to a multivendor stack as part of THIS migration, so that, if one of your new vendors goes rogue (just like VMware/broadcom did) you are not trapped again. This complicates even more the migrations, as, you will need to handle a multivendor environmet, and more so, for a while you will have to juggle 3 vendors (WMware + the other 2)
4.) For ages VMware was a model citizen, which means everyone certified agaist them. Before the migration you need to make sure all your workloads are certified. This is 4x valid for purposes of regulation, certification, compliance, and (cyber) insurance
Is a very complex issue, for many an organization is not as simple as "I migrated the VMs in my homelab in an afternon so how hard can it be?". And the timelines are heavily compressed.