Why are AV Preamps not cheaper than receivers?

Because they are more desirable, usually have better sound/build quality. I don't even know where you can get one for the prices you stated.

That's a good question. Outlaw Audio and Emotiva make less expensive AV preamps than the big companies do but one could say they are even overpriced for what they really are. One could also argue they only market such things because they want to sell amplifiers as well, which is their main product and profit center:

https://emotiva.com/collections/processors/products/mc-700

The big companies dropped AV preamps from their lineups for a while altogether and just marketed receivers for a number of years. Smaller companies like Parasound and B&K developed AV preamps independently for a while. Parasound dropped theirs altogether after they figured out they'd lose their shirts continuing in that market. B&K's development costs killed the company off. They were expensive propositions to develop.

If the question is why companies like Marantz, Yamaha, and Integra market AV preamps that are as expensive as their top of the line receivers, it's because they know people who would buy an AV preamp want a quality product. Also, selling an inexpensive preamp would cause parasitic losses in their receiver line which is where they make their money. Quality costs money. The processing circuitry and power supply in a high quality AV preamp is superior to that in what may appear to superficially be the same in a receiver. And that's where the cost comes into play, both developmental costs and materials costs.

Customers who are ok with mediocrity would most likely buy a $300 receiver anyway and be happy with it. The big companies cater to all price levels.

As for me, I stopped buying AV preamps some years ago because they are too expensive to upgrade every few years and I'm not as particular about sound quality in home theater sound as I am about two channel sound. And I have enough room for two separate systems. If I had to have only one system, I would have an AV preamp instead of a home theater receiver.

This discussion is interesting to me in that it illustrates how different the HT market economics are compared to 2-channel stereo hifi audio.

The small companies do all (OK... virtually all) of the high-end heavy lifting. Probably because licensing requirements are virtually nil; most everything's in the public domain (or proprietary -- i.e., 'trade secrets').

The 21st century concepts of innovation sure are -- interesting.

A large part of it also has to do with consumer preference and the economy of scale. Sadly many of the components in the midrange AV preamps are the same as in the receivers. Minor performance gains are often achieved by having less other electronics in the same box that can cause interference. Much of the additional cost is due to the design, marketing, and support of the equipment. The demand for truely high end multi-channel is quite limited. Literally removing the amp section from a receiver would not be that be much savings due to the manufacturing changes and tracking required, not to mention some way to differentiate the two. While I am sure some would be fine with the size for some reduced cost, many would complain it is taking up too much space that is doing nothing... might as well buy the version that has the amps (even if they never use them at least it has a better chance of a resale).

Most consumers want the included amps,and connect their speakers with budget cable for cost reasons. Explaining a person needs to purchase an additional 5-amps boggles their mind. Then come the question of where are they going to put these other amps, and wait, now, I have to buy cables to connect to each amp......

If I recall correctly one or two of the major AVR brands tried marketing 7.1 Ch, 5 amp higher end systems. They used an old chassis and amps with new AVR boards and display. The thought was many people do buy or use a larger separate amp at least for their mains. They did not sell well. There was little if any price difference between the the systems that had 7 amps. There can be improved fidelity claims, but those people truly want separates and get down to specifics. These "card" amps are made in volume and removing 2 is really only minor savings. For the masses it is easier to include them.

Oddly people are willing to pay for the addition of the pre-amp out addition to these AVR's. Many people dream or hope to run at least separates for mains even if they never use them. To others, pre-amp out is an extra cost feature and they go for the less expensive all in one that has a higher wattage output.

There is also the development cost of the chip to do all the processing and the user interface. Some of these chips, while they may have acceptable D/A quality, can create a lot of their own noise that affect other components so shielding and heat become another design consideration.