Cost questions

Is there a reason why pet owners are intended to go broke for their pets? We've spent so much money on our pet (12f cat) for her to constantly be miserable for the past 5+ years. She's just been diagnosed with colitis after 3 weeks of diarrhea, pudding consistency, and they sent us home with 80 dollars worth of food and 40 dollars worth of probiotics, which she hates by the way. She's been hiding, doesn't want many pets, but our concerns that she was nearing her end were dismissed. The vet also spoke about a deeper dive which is more poking, prodding and stress on our cat, as well as a financially irresponsible. I clearly love my cat and I wouldn't be taking her to the vet to talk about end of life things if I didn't care. But I felt like I was being given a sales pitch on Royal Canin instead of talking about the reality of her quality of life. Which is miserable. Why do I need to spend thousands of dollars at the end of life, when it's obvious. Do I just wait for her to have a natural death and let her suffer longer? Really unsure what the move is here. So any input is appreciated.