Iran are Shia and the other gulf countries are Sunni. There is a big religious gap between these and historical animosity and rivalry.

The Islamic Republic of Iran believes in exporting the revolution: https://en.wikipedia.org/wiki/Exporting_the_Islamic_Revoluti...

Basically they believe the rulers of the gulf countries should be overthrown and that those countries should be run by Islamic rules. So basically MBZ who rules the UAE (as an example) wants to keep ruling the country and strike some balance between economic prosperity and maintaining his rule while Iran would want to see him removed and his government replaced by a theocratic regime. Naturally the UAE also wants not to be bombarded by Iran but the personal survival of the UAE rulers is a bit more important to them than that goal.