They’re using their newly acquired license to TTD to hold the better remake hostage, presumably in the hopes that enough people will pay up. You can still play OpenTTD for free if you already have it on your account or download it directly from their website: https://www.openttd.org/downloads/openttd-releases/latest

You can also donate to OpenTTD, as they will receive none of the money you give Atari: https://www.openttd.org/donate