Why should Stripe take on the cost of investigating / handling a potential chargeback, even though it might be likely to be resolved in the business (and Stripe's) favor?
When it comes to chargebacks it's not just customer experience (reputation damage due to fraud) and liquidity risks that Stripes or other payment providers are protecting themselves against - but also the actual support cost of handling each chargeback too.
Chargebacks are a possibility with every single credit card transaction. Routine B2C transactions carry the possibility that a card number was used fraudulently, the product was never delivered, or the customer is otherwise unhappy. A one-time payment for a vehicle with a state-documented title carries none of those risks.
So let me get this straight, you're siding in favor of Stripe not doing what Stripe signed up for by becoming a payment processor, is that correct?
Not correct, OP entered into an agreement with Stripe where Stripe would process payments received for the sale of cell phones (and not automobiles).
It's also not terribly surprising that someone who develops familiarity with one tool will then apply that tool to new situations. The main problem here is the ever-growing financial censorship regime / decommodification push that insists companies should be prying into their customers' business.