In 1983, a 1541 cost $299 MSRP and Commodore had a very difficult time keeping up with demand.
I flipped through an early 1983 issue of InfoWorld, and couldn't find a price on a genuine Apple Disk II, but two vendors were selling aftermarket Apple-compatible drives for $299. One quoted a retail price of $479. So that tells me the retail price on the Apple drives had to be higher than $479, otherwise there wouldn't have been a market for the clones.
Commodore's thinking was that not everyone would buy a disk drive, so they built the intelligence into the drives so you didn't pay for stuff you didn't need. Had the VIC-20 and C-64 had the disk controller built in, they wouldn't have been able to hit the initial $299 and $595 price points at release. That did mean additional drives cost more, but the majority of Commodore owners stayed with single drives. And in spite of the added complexity of the Commodore drives, they still were priced competitively with Apple.
As for the captive audience, the supply problems and frailties of the 1541 worked against it--some people wanted to buy anything but a 1541. But copy prevention reduced the compatibility of the third-party drives. And most of the third-party drives had their own problems. I had a good friend who replaced his 1541 with an Excelerator+ drive, which was regarded as one of the best aftermarket drives. He had more reliability problems with it than he had with his 1541. The Excelerator was nice in that it was really small, it cost $50 less than a 1541 did, and the compatibility was pretty high, but he had to send the thing in for service a two or three times and that pretty much wiped out the cost savings.
The people I knew who tried other aftermarket drives (Blue Chip, Indus) weren't enamored with them either. The couple of people I knew who had MSD drives were happy with them, but people who were buying MSDs weren't looking for full 1541 compatibility. They were looking for the additional features the MSD offered, and were willing to live with less compatibility and a higher price.