You do realize the very first post in this topic is about the decision to port the Linux version of the engine to the EE branch of code, since it was not feasible to do both the current release branch and the EE?
The money pledged by Linux users was used for the Linux version, the budget for which was greatly increased due to issues with middleware, etc.
The console versions, funded by a publisher and proceeds from Windows/Mac sales of D:OS, had an extra certification process that it needed to go through, as well as manufacturing for the retail release. The PC versions of the game are digital only, and therefor had a more flexible release, which did not need to be determined as far in advance (and it was only fairly recently that Larian was confident the Windows version would be ready by the console release).
Without separate teams for every platform, the only way the game could be completed was to do the content first and focus on the console versions. When they got sent for certification, start switching over to the Windows version to focus on PC only issues (changes to the keyboard/mouse UI, etc), then port to Mac and Linux. The plan was to have that process done for a simultaneous release, but it took longer than anticipated.