Pay. The auto industry on a whole pays not just less than FAANGMULA, but also less than banking, telco, and consulting.
Source: I've worked for the automotive industry for ~20 years, on and off.
So it's just bad accounting?
All these big auto companies like VW, GM, etc. used to do in terms of SW dev is write the spec and requirements and then contract out the dev work to the lowest bidder (Continental, Bosch, Valeo, Denso, etc.)
first, the software is traditionally up-front cost, development cost, and as such it's not accounted for in the production cost aka BOM of an individual vehicle.
but even if you'd jump the accounting hoop of spreading the software costs to the vehicles it's neclegible compared to other cost factors.
VW group builds 10mio cars a year. the core ECUs board computers are shared across all models and makes. a major revision happens every 3-4 years. that's 30-40 mio units you spread the software creation costs to.
the major cost (as in 90% of that) is going to be silicon, PCB, housing, the physical part. and share of ECU costs in the overall vehicle costs likewise is in the low 2 digit percentage, should it even reach that.
the accounting makes sense.
The whole "industry pay isn't low, I know someone who's a millionaire, you're underpaid" alone doesn't really help anyone without any hard facts.