You can certainly say “saya tidak menolak” (= “I didn’t refuse” or “I won’t refuse”) but using “bisa” (“can”, or “able to”) adds extra meaning. It’s really the same in English: “I won’t refuse” is different to “I can’t refuse”.
Yes, thanks for clarifying. I meant the verb that tidak is negating in this sentence is 'can', but maybe I could have been clearer. Without bisa you can still negate menolak with tidak, but as you said it becomes 'did not refuse' rather than cannot