Drugs are an interesting case as they have these factors going for it:
1) Expensive to bring IP to market. Lots of testing and clinical trials for drugs. For SW it is pretty cheap now.
2) Easy and cheap to copy. Generic versions can be reverse-engineered quickly. Probably just as easy to copy software, but I still feel like this is probably a useful pillar.
3) The IP by itself constitutes the majority of the value of the product. In medicine there isn't typically tons of other IP around that come together to form the product. In SW there is rarely a single piece of IP that is more than a small fraction of the value of the product.
4) The IP has longevity as a standalone product. Viagra can be sold for decades. Aspirin still probably does hundreds of millions in revenue. There is little SW IP that, by itself, has longevity. The nature of SW is to continuously improve it.
5) Time to market isn't a huge advantage. Since most medicine is just sold as effectively a commodity, being 6m ahead of your competition usually just means you have 6 extra months of revenue. Whereas in SW it also means that gives you 6 months to build on your current IP. In medicine you don't typically do Viagra 2.0, with a boatload of new IP that makes the original obsolete (and hence any competitors shipping the old version scrambling).