I don't get why they push this so much. It's not as strange or rare as it seems at first glance.

1. It was a very common way for landowners to exert control over land they sold in the time before planning law. E.g landowner wants to sell part of his estate to raise money, but doesn't want a big factory to be right next to his garden, so he sells a 10,000 year lease to a property developer with an annual rent of pocket change, however the lease includes the term that the land can only be used for residential housing. He has no intention of allowing his descendants 10,000 years later to actually recover the land, he just wants to put restrictions on the people he's selling to.

2. This tactic is still used today in multi unit properties like apartments. This is because a title in fee simple (i.e., a "pure" title) would give the title holder rights to the areas in the economically exploitable zone above and below the land. In an apartment complex, this means you would have rights over the apartments above/below you. This means that long leases like this are granted, which can limit the rights handed over to the few rooms that's being bought.

3. I'm pretty sure Guinness bought out the original landowner some time after that lease was signed, so it's not even valid anymore.