As a user it is because I can no longer use the subscription with the greater tooling ecosystem.
As for Anthropic, they might not want to do this as they may lose users who decide to use another provider, since without the cost benefit of the subscription it doesn't make sense to stay with them and also be locked into their tooling.
No one said it was complicated, and you might be imagining that I care more than I do. However if you can't understand why having a feature of a paid product removed is dissatisfying, then I cannot help you understand any further.
I am surprised that anyone would think the "product" is the web interface and cli tool though, the product is very clearly the model. The difference in all options is merely how you access it.
Feature, attribute, loophole. I really doubt we fundamentally disagree on the situation here. You can use your empathy to understand why people are disappointed, and I will pretend such a detail oriented thread has made me feel content. Anthropic can do what they want, it's their service.
As for Anthropic, they might not want to do this as they may lose users who decide to use another provider, since without the cost benefit of the subscription it doesn't make sense to stay with them and also be locked into their tooling.