Here's the question — How would combat work without opportunity attacks? It virtually asks "why games need opportunity attacks and what happens if we remove them".
It was asked in context of D&D 5e, thus attracted answers and comments about OA-based game features in 5e (like Sentinel feat, etc), which would become less effective or completely useless without OAs.
But these answers are obvious — there are OA mechanics in game, also there are features based on these mechanics, so if we remove OAs these features becomes meaningless. I actually wanted to ask another thing — why OAs are there in the first place?
So I've edited the question in order to make it more system-agnostic. Downvotes and VTCs appeared, presumably because it is a question about designers' intent now, therefore off-topic. But I don't think the reason for OAs is a particular designer's intent. OAs are ubiquitous, so I guess there must be an objective reason for them to exist in TRPGs and wargames.
What is the main problem with this question and how can I fix it to attract more high-quality answers?