If this was the only flight that day it would be a great question; but it is not.
The Daily Mail, UK, has an article that says there are 300 flights over the Ukraine on a DAILY basis. Your map shows none of them, and if any actually flew over that part of the Ukraine, but with 300 a day, I’m sure there were probably a few.
The reason to fly over this airspace is very apparent when one looks at a world map. The direction from a Northern European airport to Kuala Lampur or Singapore takes the flight over Southeastern Ukraine. Direct flights save a lot of avgas, which cost the airlines money. There was no doubt a financial imperative to save avgas for this cash-strapped airline. Well, now there is a financial imperative to avoid that airspace. For whatever reason (probably money again), the airlines thought that flying at at least 10KM (34,000 ft) would be safe even over a civil war.
At the altitude they were flying, one could argue it would be unreasonable and illogical to expect any SAM weapon system capable of shooting them down, were also incapable of identifying them as a commercial airline, and hense not a threat.
Russian terrorists in Ukraine drunkenly played with some seriously dangerous big-boy toys, provided to them by Putin.
Expect more of this type of stupidity worldwide.
There is a reason we fought the USSR in the “Cold War”, and a reason we won that one.
Those people are both utterly vicious and utterly stupid.
It was the stupid part that allowed us to prevail.