The very short explanation is that they kind of want to be not-Saud and has trouble cooperating with Saudi Arabia for a rather long time, not just over fossil fuels but also in Yemen.

Recently the UAE faction in Yemen was forcefully reined in by the house of Saud, and OPEC kind of prioritises different things than the UAE, i.e. not pushing profits hard in the short to medium term instead focusing on stability and predictability.

Currently the saudis are trying to resolve the Hormuz issue and the attack on Iran through diplomacy, which the UAE is not exactly fond of and would rather see a violent solution. In part this is coloured by the close relation between the UAE and Israel, both of which share the view that running militant factions in failed states is preferable to orderly international relations between sovereigns. The saudis aren't as keen on this type of foreign policy and in other aspects also not as friendly with Israel as the UAE.

The UAE has been signaling that they don't really want to be a part of OPEC since at least 2020 or so. Them actually leaving was to be expected, the question should have been 'when' rather than 'if'. Iranian retaliations on the UAE and subsequent damage to the reputation of mainly Dubai and Abu Dhabi as well as capital flight probably strengthened the UAE politicians longing to get out of OPEC and start pumping and selling at full capacity to try and make as much money as possible as fast as possible.

If the UAE does not do this it'll be more exposed to credit and currencies besides the US dollar, which they probably find rather inconvenient.