The point is that a browser that can view the modern web is different than one that can run a 10-year old intranet app. These are very different things. I agree with you that corporations sometimes need both.
Since there are open source browsers, you can just save a very old version of them for intranet apps, if you must. But you can't expect a modern browser to still run your old intranet apps, you will need both a legacy browser and a modern one.
The ESR fits somewhere in the middle. It won't run 10 year-old apps, but it will update very slowly so your IT department does not need to constantly verify it (only once a year). Again, for 10-year-old apps, that won't work - you just need to install a 10-year old browser. If you just run it on intranet apps, security isn't a concern so that's fine.
Since there are open source browsers, you can just save a very old version of them for intranet apps, if you must. But you can't expect a modern browser to still run your old intranet apps, you will need both a legacy browser and a modern one.
The ESR fits somewhere in the middle. It won't run 10 year-old apps, but it will update very slowly so your IT department does not need to constantly verify it (only once a year). Again, for 10-year-old apps, that won't work - you just need to install a 10-year old browser. If you just run it on intranet apps, security isn't a concern so that's fine.