You answered your own question: they want to have the opportunity to maximise earnings per customer by attempting to find the maximum each and every customer is willing to pay. This can only work when the pricing structure is opaque. It is one of the reasons why I shun products and services which require me to contact the vendor to find out what they expect their customers to pay.
Hell, I assume this is only popping up after seeing Matrix eat their lunch and being chosen over them for the German Armed Forces, French government, and German healthcare system.
Different organizations have different requirements, so they choose different solutions. Threema Work is used by the Swiss government, Bosch, Daimler and others.
Threema and Matrix are quite different. Matrix is a centralized / federated system where data is stored on the server. Threema uses a decentralized protocol, where data and metadata (including groups) are stored on the devices only. This has advantages and disadvantages, depending on your requirements.
I see: it's not for free.