The 3e version of the spell specifically summons the ally from your deity, UNLESS the cleric has no deity, it which comes from a being that aligns with the clerics philosophy instead.
This actually explains why the 5e spell is written the way it is. Its easy to forget that some clerics (abit not ones in FR), don't worship Gods at all, so being able to ask help from other cosmic beings instead of a God makes sense for them. You could even expand this logic to Clerics of deities, who turn to cosmic allies of a God for specialized help.
So mystery solved.
This actually explains why the 5e spell is written the way it is. Its easy to forget that some clerics (abit not ones in FR), don't worship Gods at all, so being able to ask help from other cosmic beings instead of a God makes sense for them. You could even expand this logic to Clerics of deities, who turn to cosmic allies of a God for specialized help.
So mystery solved.