The reason Opinion Based (OB) is used too frequently to close questions. Two examples:
Why are long distance trails so much more famous in the US than in Europe?
What top items did the teams competing on the TV survival show Alone most frequently choose?
Neither of these has been closed, but both received VTC.
In the second case, the VTC probably came from quick, sloppy reading. As @Charlie Brumbaugh said:
How is this opinion based? If this was asking what 10 items to bring it would be, but this is asking which items they do choose and hopefully that information is recorded somewhere.
In the first case, I postulate that the OB VTCs came from people who did not know much about European long distance trails, and so it seemed OB to them. However, a person knowledgable about European trails gave an objective answer, backed up by pertinent information. As I commented on the Q:
this Q is not primarily opinion based; the accepted answer demonstrates that there is a good objective answer to this question.
There are many more examples I could find, but it would take a lot of time.
So, my plea is:
Read a question carefully before you VTC.
Don't assume because you can't think of any but an opinion based answer that a person knowledgable on the subject cannot write an objective answer.
Of course, there are opinion based questions. With apologies to @James Jenkins, if he had asked
How should I cut my toenails on the trail, with a nail clipper or with my multi-tool knife scissors?
that would have been opinion based.
Of course, JJ's question was different, but there have been similar questions on TGO properly closed at OB, but I do not have time to search for them.