The only reason Wikipedia can do that is because it's at the top of 50% of all Google search results. Constant epic scale exposure that Wikipedia has been able to use to push for donations (and further to build up a routine of it, an understanding of how Wikipedia operates, to millions of people). Realistically Arecibo has nothing like that to leverage. Donating to Wikipedia is a value to action instant feedback process: you land on a nice and helpful Wikipedia page, you derive value, you give some value back; again, Arecibo can't offer that kind of in the moment, click of a mouse, value-donation gratification to large numbers of donors. Arecibo's donor pool is mostly the Paul Allens of the world.

TLAs have lots of money.