Stop thinking like content creators for a second. Put yourself in their shoes. I work on an executive board for my main line of work, and you would be surprised how much strategy is constantly discussed to ensure the survival of a company. I can guess how some of their discussions went. Also, this player is done. It's not like customers complaining will stop them using it unless they take a huge sales hit, and there are no indications that has happened or will happen.
Spitfire as a company is sinking a HUGE amount of money into content creation and overhead to support the company. The libraries are getting bigger, they are taking on partners on libraries, and their goals are becoming more expensive to execute on. On the NI platform, they have very little control of new features, what NI will charge for licensing, how they choose to support the product, and the copy protection scheme on Kontakt which is certainly not an elegant solution. For small and middle sized devs, all this is acceptable to avoid supporting a whole platform. When you get to the Spitfire Audio, Orchestral Tools, etc level - it's just too large of a risk to put your entire business model in the hands of a company that just laid off 30% of their entire company while also NOT heavily reinvesting back in that platform. If anything, I would see NI as a company spending more money as a competitor in that space, than as a developer making a better application ecosystem. Sharing their sales numbers gives away another competitive advantage to NI. At some point the trade for risk associated with moving away from Kontakt as your main platform is smaller than the risk of developing your own.
East West's play engine while being much worse than Kontakt, allowed the company to move forward with a cloud based product that is providing sustainable and predictable monthly revenues for the company. That's what they felt had to be done to be a modern company that could thrive, and it's worked out well for them. They have a competitive advantage despite the play engine not being great.
Orchestral Tools from the looks of it, already have some novel features in Sine that will allow features Kontakt has been too lazy to add because it would appear they are mistakenly not working with developers to find out what they and their customers need. From what I've seen, we want easily downloadable libraries we aren't worried about losing after a drive crashes, something managed in the cloud with easy updates, the flexibility to not download every part of a library, the ability to make our own mixes to save resources, a UI that gets out of the way while allowing for expression and organization, decent under the hood features like good filters/envelopes/FX/extensible scripting if possible, and the overall respect for system resources that the platform is purpose built for the way composers work that takes into account some level of portability.
It will be interesting to see how Spitfire Audio choose to handle the customer reactions of their sampler platform. Criticism doesn't mean it's bad platform. What they are trying to do is hard, and making moves like that are complex no matter how well planned and intentioned. I think there is also a loud minority of people who take to the internet to complain. Give them time, and I think they will improve the UI, performance, and add features customers want. Just be realistic, because while I am a huge fan of NI, look how long it took them to get to where they are while missing some features Spitfire has already addressed, like library management and content delivery.