Part of the reason for the difference is that some cultural entities can grow very large and powerful. In particular governments can get vary large and can survive for hundreds of years. One of the common results is government-granted monopolies. Copyright, trademark and patent laws deliberately seek to establish monopolies. These laws form the basis of many modern monopolies.
Another issue is the successful suppression of parasites. One of the reasons why cultural entities can grow so large is that parasites fail to take them down. The equivalents of hospitals, vaccinations, quarantine and medicine are at work to suppress parasites, reducing their ability to take down highly successful cultural entities.
Organic monopolies are not common, but we can see what they look like a bit by looking at agricultural monocultures. These are partly the product of human culture, but are made primarily from DNA genes - rather than memes. Agricultural monocultures do have problems with parasites. As we see in the cultural realm, they rely on parasite suppression techniques to remain viable. Agricultural monocultures exist partly because they offer advantages. In particular, support becomes easier, since only one genotype is involved.
Are there corresponding advantages for cultural monopolies? Advocates would argue that there are. Monopolies result in giants, and having some giants on your team helps in cross-team competitions. One problem with this line of argument is that it isn't clear whether monopolies do in fact result in giants. Monopolies do fairly clearly result in inequality, but you can still have giants without a few powerful folk being in charge.
One oft-cited reason for allowing monopolies is that they are of limited duration and they provide an incentive to avoid trade secrets, which would result in less sharing overall.
Having laws that promote monopolies and then more laws that make complete monopolies illegal seems like an odd way of managing things. Superficially, it looks as though lawyers are making work for other lawyers, at the expense of everyone else.
The future of monopolies is an interesting topic. Some have speculated that in the future there will just be one big monopoly. This would be rather like the "empire" in Star Wars. Whether something like this will ever happen is not yet clear.