I'm looking for some expert advice because I'm at my wit's end.

I bought a Specialized Sirrus 2.0 one year ago (Specs: specialized.com/us/en/sirrus-20/p/200206?color=322026-200206). It's a road bike, and I'm using it for my commute in any weather.
Ever since, I've been having issues with the disc brakes losing their grip. Currently the breaking power is significantly diminished on both brakes, and they squeal as the bike comes to a halt. Cleaning the discs with Isopropyl alcohol sometimes helps, but the issue comes back quickly. I've been having this issue many times now, and I've usually ultimately addressed it by switching the rotors and brake pads (probably done that ~5 times already now, either my self or in a store). I'm about to change the rotors and pads again, and I want to figure out what the root cause is so I don't have to change them again in a few weeks.My understanding comes from what the people in the bike shop have told me. I'm told this issue comes from some grease/oil contaminating the rotors, and the oil doesn't come off once it's baked in after braking a few times. But I don't know how oil might get on there. I don't touch the disc rotors with my hands, and I try to avoid riding through puddles in the street when it's raining. I haven't been using any oil or chain lubricant on the bike. I've been buying cheap no-name rotors and resin pads on Amazon.
I've had the suspicion that the hydraulic brakes are losing breaking fluid, and the store switched out the rear brake system, but the issue persists.

Does anyone have an idea how I could solve this?

I have been spending so much time and money on fixing what should be a new bike with less maintenance effort than my old one with rim brakes. Thank you, I really appreciate the advice.