Washington Post:

The Houthis are the most committed, the most ideologically pure and the most aggressive of Iran's regional allies.

The internationally recognized government in Yemen is fragmented, weak, fragmented and corrupt, and the Houthis have been able to systematically exploit this.

The Saudis seem reluctant to engage in another all-out war with the Houthis, as any ground campaign would lead to prolonged fighting and heavy casualties.