Because they are relatively new in the automotive world. I can take my '08 CRV to just about any auto parts store in America and get just about any part I need (or take it to about any third party repair shop with the same results). Good luck doing that with most EVs especially Teslas. Tesla is the most egregious example as they are anti right to repair and have seemed to take a page out of Apple’s book as far as locking down their supply chain for parts.
Hopefully this will get better with time as third party shops have time to acclimate themselves and their technicians to EV architecture, and EV-specific parts become more available. Though the latter I feel is highly dependent on manufacturers not trying to turn EVs into phones in terms of repairability/serviceability.
In the meantime, as an average Joe without a lot of money, I really like the idea of keeping my relatively low cost older ICE vehicles because if shit hits the fan, if I can’t fix it relatively cheaply, there will likely be multiple shops that can without it costing me an arm and a leg and/or taking weeks or months to wait on the manufacturer to supply the parts needed.
This is reductive