That's a good point, but here's my guess (no inside information) on their decision process --
Sam's Town is a sprawling property, with casino, hotel, multiple restaurants, bowling, RV Park next door, and more. And an established following -- a mix of locals from the area, plus mid-price / value-oriented tourists.

And I'll bet it is profitable and cash-flow positive too. Also, it IS named after SAM Boyd, the founder and namesake of this property AND the Sam Boyd's California Hotel downtown. Bill Boyd, his son, was CEO of the company and now Chairman Emeritus, and major shareholder, though Boyd Gaming is a publicly traded company.

They probably had already written off Eastside Cannery completely, or just carried it on the books for its land value, so the demolishing cost and eventual sale to a home developer won't cost them much (and may even be net-positive).

One last thing -- by selling to a developer, this parcel that's currently zoned for a casino will forever be unavailable to other casino operators in the future, which will remove a nearby competitive gambling location near Sam's Town. As they say in real estate, it's "location, location, location."

Just my two cents.