The main objective is to neuter the Iranian regime to diminish how threatening it could be to Israel, behead the government, destroy military targets, destroy its lifeline from the oil industry. If regime change happens because conditions worsen it's a good bonus but without forcefully removing the regime with boots on the ground it's just wishful thinking that it's the main objective.
Iraq was also under a brutal dictatorship with Saddam, it took more than a decade of ground operations to actually change it. Iran is more populous, has a much more loyal regime security force, is more ideologically driven, and has a much worse geography for any ground invasion.
When the bombing stops there will be so much destruction that the regime can point towards the USA and Israel that it will keep having loyalists behind to defend them, the IRGC will absorb the more loyal ones and grow to keep stamping out revolutionaries.
