[quote=@duck55223]
Without spoiling to much, human-like and humanoid aliens being common makes sense.
[/quote]

There is the argument to be made that two arms and two legs is typically more efficient as far as biological energy goes. There may also be other points about the dexterity of hands allowing for the work of fine tools lending to advanced development, never mind more effective tools to help harvest or acquire energy-rich food that would benefit the development of the race down the road by providing nutrients that aid in rapid growth or some such.

I don't claim to be an expert on biology, let alone space biology but as I've gathered this is the basic theme. You could have a highly developed brain like a dolphin's but it's not going anywhere without fine tool manipulation, nor being capable of entering and taking advantage of the open biological niche to be occupied by human-tier intelligence.