Would Musk focusing only on it make any difference?
edit: This is not a complaint, just a question, why the downvotes? I'm used to getting downvoted for no reason, but this is basic a question, with great answers. Come on HN! We can't ask questions?
One, this is his baby. I believe he spends more time at SpaceX than his other companies. Two, B2B. The public only sees breathtaking videos. The contract negotiations, sales process, pricing, support, insurance, et cetera happen behind the scenes. Finally, nothing has been on time. Years' delays don't feel that bad because (a) space is hard, (b) space is awesome and (c) everyone else going to space is even worse at keeping to timetables.
Landing and reusing the Falcon 9 cores is probably a much bigger benefit to their bottom line overall.
Tesla on the other hand has to be able to deliver tons of reliable cars to people all over the place in a competitive market. Delays to the Model 3 mean they're burning money they can't afford to lose while their competitors are rapidly catching up to them.
While SpaceX could continue their successful Falcon 9 launches during the 5 year delay on Falcon Heavy, Tesla will likely be gone in 5 years if Model 3 delays are even close to that long.