It isn't those patents specifically, but the IP developed on top of the safe harbor that those additional patents provided at the time.

It is difficult at any particular point in time to develop IP in this space without infringing patents that are still in force, because even if you go back and base your work on patents that have expired, unless you are very careful and clever you will be infringing on newer patents that are themselves also based on those expired patents.

You may be able to show that some of the key claims of those newer patents were "obvious to a person having ordinary skill in the art" and/or come up with prior art to give yourself some wiggle room, but that's a lot of effort with an uncertain result.

A surer strategy is to patent new developments on top of current IP that, while you can't use them without licensing the original IP, neither can the holder of the original IP, and if your new stuff is in their critical path and engineering around it would be annoying enough, you may be able to get them to negotiate a cross-licensing arrangement or something similar.

IOW, if someone's moat is stopping you or their tolls are too high, start digging a moat around their moat to get them to cut you a deal.

It's still tricky though: you can't patent stuff too far ahead of where the original IP holder is going because you may guess wrong about where they (or the industry) is going to have to go, or even if you're right your patents may expire before they become important (and you ran out of money to keep building more IP on top because your innovation wasn't implementable yet or you were too early to market), and if you aren't far enough ahead you run the risk of them patenting whatever innovation you are working on before you do, or even having the "obvious to a person with ordinary skill in the art" shoe on the other foot (and their legal department is bigger than yours).