What the hell kind of answers were you expecting with the question you asked?
Average years of education for a doctor: 8 yrs
Average years of education for an interior designer: 6 yrs
Average on-the-job training before you can call yourself a doctor: 3 yrs
Average on-the-job training before you can call yourself an interior designer: 3 yrs
Average student loan debt for a doctor: $140,000
Average student loan debt for an interior designer: $55,000
Average starting pay for a doctor: $140,000
Average starting pay for an interior designer: $35,000
Average median pay for a doctor: $350,000
Average median pay for an interior designer: $50,000
Average billable rate for a doctor: $400/hr
Average billable rate for an interior designer: $100/hr
Average annual continuing education and dues for a doctor: $1,000
Average annual continuing education and dues for an interior designer: $1,000
So as you can see, the problem isn't interior designers charging too much, it is customers like you being too cheap to pay for the service you receive. If you are a self-avowed cheapskate who wants nothing but mass-produced crap from chain stores, then you have no need for an interior designer anyway, so it doesn't matter how much they charge.
The nice thing about interior designers, if you decide you don't want their services, you won't die. Whereas a doctor makes a handsome profit off of you having little choice but to pay their extortionist prices.