Why are Essentials and Showcase Presents so expensive?

[MajorHoy]

It's simple supply & demand, people!

If they are no longer being produced, then we start having a limited supply.

As more people start looking for them, demand increases.

Whether prices some people are asking is "reasonable" may be a different question, but if there are fewer options available, it all comes down to what somebody is willing to pay for what's available.

[RamblingMan]

I suspect a lot of collectable stores (record, books, comics etc) will look online at ebay type auctions and look at what people are selling items for at the buy it now option and assume that's what the market is for a particular item. Look on amazon where people will try selling an omnibus that is OOP for $1000+. Oftentimes people will overestimate what the actual market is. The lesson for an individual is to not buy what was intended to be a cheaper copy of an item. Go buy some newer, better produced, color accurate version for the same price or cheaper. At the end of the day these aren't original collectables. They are copies.
There will always be people though who want to complete their collection in the same format.