Why isn't there a link to a compiled Windows wallet? 
Because I/We are not the original developers of GRE it's hard to explain reasons or motives behind why the original developer/s made the decision to scale down the 
grcoin website to a homepage. 
Archive.org shows us that grcoin was quite an extensive CO2 offset cryptocoin website, which was quite innovative...
ARCHIVE.ORG's FINAL WEBSITE IMAGE of GRCOIN in 2016: 
https://web.archive.org/web/20161201105230/http://www.grcoin.com/pages/helpSince December 2016 compiled GRE binary download links for Windows, Apple Wallets, etc. were removed as well as direct download links from file sharing site mega.co.nz - GRE download files are removed.
Perhaps it's because they could no longer support the Greencoin project. By removing all Binaries and only making source available, they could help future GRE price by limiting the amount of users overstaking GRE supply yet by making source available the project could be revived at any time by new developers.
In our testing late 2017, we were successful when compiling existing GRE v1.2.1 source code into Windows Binaries - this was/is not a problem to produce. 
However, the decision to publicly release the private key of the GRE foundation wallet is a perplexing action and state previous developers have left GRE in - which in ideally needs to be resolved in order for GRE to provide an attractive proposition again to returning business and investors.