This appears to be due to the fact that they have "identified an issue in the PC version that can cause the game to crash for players with certain GPUs." This issue has forced them to make the difficult decision to delay the game indefinitely while they find a fix to this issue.
"We will communicate the new launch date as soon as possible," said the development team.
Although the PC version was delayed indefinitely, the announcement also states delays for the Xbox, PlayStation, and Stadia versions. The date has been pushed back two weeks to March 23rd due to issues found in these versions.
Even if this news may be sad to those looking forward to playing multiplayer on Legion this month, it is good to know that Ubisoft is taking steps to make sure the game is ready for release instead of releasing a broken update. In my opinion, that would only frustrate players even more!