The Houthis are also united by tribal loyalty to some folks who ruled Yemen for 1000 years until 1962, so they have older, more establish legitimacy than Ibn Saud ever did. They just don't have the money.
But in the poor hinterlands of Saudi Arabia there are tons of proles who aren't part of the royal family and aren't getting shit. The Saudi government strictly prohibits anyone from going into these villages and interviewing people or doing news reports on them, because they are hostile to the Saudi government.
So it looks that's why the Saudis were persecuting the Houthis in the first place. It started with them going after one family that had connections over the border in Saudi Arabia: https://en.wikipedia.org/wiki/Al-Houthi_family
The Saudis are afraid this family can form a bunch of tribal relations with Saudis in the countryside and displace the Saudi royal family. It would become Houthi Arabia all of a sudden. That's what Saudis have been afraid of this entire time.
On 10 January 2020, U.S. Secretary of State Mike Pompeo announced plans to designate Abdul Malik al-Houthi, Abd al-Khaliq Badr al-Din al-Houthi and Abdullah Yahya al-Hakim as Specially Designated Global Terrorists.[26] The following year, Antony J. Blinken revoked the designation.[27]
On 16 May 2025, during the context of the Gaza war, Israeli Prime Minister Benjamin Netanyahu and Israeli Defense Minister Israel Katz warned al-Houthi that if his group's attacks on Israel continue, he will be directly targeted and "hunted down and eliminated," saying that al-Houthi could "join the list" of Hamas leader Yahya Sinwar and Hezbollah chief Hassan Nasrallah; both killed by Israel.[28][29]