Because your tank sucks....
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just kidding
I have a 24g nanocube and at one time had a similar stock list (Neon goby, Clown, Flame Angel & YWG). Loved the Flame but it died for some unknown reason after a month. Never had a clown goby, their reputation for laying eggs on SPS corals was enough to make me rethink them.
Nice looking monti cap, I have a purple one and a green with blue polyp one, nice corals that grow very fast.
What are your future plans for this tank? More SPS?