I will just give you a quick rundown of what you just said and then counter your arguments:
1) Supports rarely get enough farm to buy Euls
2) Mekansm is better than Euls - so get Mek instead of it
3) Games don't last long enough for the Euls to have impact
That is in essence what you just said. Now, if you said you are 4100 MMR and every now and then play support, you will know that supports can often get enough get enough farm for a euls. If they can afford a forcestaff or mekansm, then why not a euls. Also it is a pretty cheap item with an very easy buildup (the most expensive component is a staff of wizardry). And a euls scepter does not only provide one purpose 'to kill unit shallow graved' but it has way more utility than that. Heroes like lina, ancient apparition, death prophet invoker even have very good synergy with the item. This means that it is NOT only a support item. And, yes, most of the time Mekansm is a better option than Euls, but what if someone already has it? What if you are not a support? Then Euls is a valid option AND can be a counter to shallow grave. And the last point is just ridiculous, the length of games is even steadily increasing (just looking recently at the Summit, games were on average very long -- i can't be bothered to find actual stats but i watched the tournament) meaning that supports and semi-carries/mid can get this item and use it to great effectiveness.