After wasting space on OUR disks for decades...
... storing all those C drives with the most useless, vulnerable or plain redundant legacy programs that end up part of their OS footprints, even if the installer chose the lightest options, they decide NOW is the time to put Win Server on a diet. Oh wow, it's taken them a long time to hear their customers screams.
Why was all that not optional on day one (or at least 3.11, NT3.5, 95, 98, 2000, XP... ).
But no, we'll just waste everyone's time on waiting for those old x86 machines to clunk through decompression and installation of all this software they won't need. After all these years! All this time wasted! And even in 2017 it's hard to keep all their unnecessary services and bloatware disabled, let alone remove it without risky, invasive procedures that are likely to cause a problem later.
MS are late to the party by >20 years, but welcome nonetheless.
Will they now wait another 10 years to roll out these learnings in a full-featured installer, or an OS you can add services & software to when you actually want them? Perhaps even one that can read existing, non MS filesystems?
Perhaps. But they'll bias it so that the only real choice for a normal human will be a cloudy one that makes MS plenty of coin to pay for their own Skynet on Azure.
Which come to think of it, maybe why they're trying to save space already!