Why is alliance restricted to one per type?

Hi,


As the title mentioned, we currently can only form one type of alliance with one civ. Why is it made so?
  I always like to form economic alliance with anyone nearby to gain more gold, or form both science + economic allaince with one neighbor.
I really dont want to form cultural alliance with anyone if I am playing a cultural game, but there isnt a choice.
Just like the research agreements, why can't we form various allies?


Please help.

I didn't find the right solution from the Internet.

References:
forums.dgbnmtics.com/threads/
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Thanks