Crapware isn't an expense, it's a source of revenue. Think of it like the ads on Google's result page. Just another conduit for commerce the carrier and manufacturer use improve profitability.
Deciding to kill a source of revenue, whether it's more appealing to the consumer or not, becomes harder to justify when that source of revenue is paying off creditors and funding new development.
A gigantic source of high margin incremental revenue. If Dell generates one signup to $ANTIVIRUS_MAKER_FOO, that can be worth about as much as the sale of the machine to Dell's bottom line. (For these and other scary insights, I suggest attending shareware conferences.)
The ads on Google's result page bring in about 75% of their revenue. If it's like that for telecos and crapware, they no wonder they don't want to lose it.
When I referred to spending I was thinking more about carriers taking responsibility of writing the custom apps, testing and distributing the OS updates etc. If they let the manufacturer do that (like Apple) they would have less stuff to bother about.
As far as crapware goes - yeah it might be ad like revenue but I can't imagine it's a major part of revenue for carriers - they can mitigate it by charging little more for the clean experience models.
Deciding to kill a source of revenue, whether it's more appealing to the consumer or not, becomes harder to justify when that source of revenue is paying off creditors and funding new development.