Regardless of whose estimates you read, OSS is a multi billion industry. However, based on the relatively infrequent signing of new vendor deals, it’s safe to say that only a very small percentage of those billions are ever “in play.”
In other words, OSS tend to be very sticky, in part because they’re so difficult to forklift out and replace. Some vendors play his situation extremely well, with low install costs but with strategies such as “land and expand,” “so sue us” and “that will be a variation.” These honey pots hide the real cost of ownership.
Cloud IT architectures such as containerisation and microservices can provide a level of modularity and instant replaceability between products (ie competition). When combined with a Minimum Viable Product mindset rather than complex, entwining customisations, you can seek to engineer a lower lock-in solution.
The aim is to ensure that products (and vendors) stay in-situ for long periods based on merit (ie partnership strength, functionality, valuable outcomes, mutual benefit, etc) rather than lock-in.