Of course they would? Millions of euros of tax revenue sounds like a pretty compelling reason to me. This is why Micro$oft's "lobby efforts" should be labeled as what they are: Nothing more and nothing less than corruption.

It takes more maintenance than Windows.

If you create your own distro, yes. But there are countless noob-friendly distros like Mint, Ubuntu and Fedora that they could use with practically 0 maintenance required. Also, compare the 2004 desktop Linux experience to now. Having used Gentoo Linux compiled from a stage 1 tarball back in 2002, I can tell you: the differences are tremendous. Many of the issues they had can be directly attributed to OpenOffice and it's bad compatibility with Microsoft Office file formats, which has long been replaced by LibreOffice. It still worked out pretty well for them, over a period of 13 years. And it saved the tax payer millions of euros of Microsoft's stupid licensing fee for their proprietary garbage.