Militarily speaking, shipping is something that's ideally a zero-risk operation. Choke points like the Strait are so dangerous because you can ratchet up the risk however you want. The optics at the beginning of the war was that Iran's Navy had been decimated and traffic threat would be negligible - as time goes on, Iran's Naval forces have effectively demonstrated that the risk to shipping is fairly credible.

The tactics the IRGC has used most effectively are small, light attack watercraft that can be hidden and deployed from austere shorelines, as well as Shahed waves from their substantial stockpile of drones. The US Navy could defend these strikes at a significant cost to taxpayers, but it's possible Iran would escalate with suicide UGVs similar to how Ukraine has attacked Russia's Navy with the Sea Baby/MAGURA drone. Military escorts would get extremely expensive and waste a lot of America's AEGIS missile magazine depth.

There is not a good way to "guard ships on the sides" against hundreds of Shahed drones or small seaborne drones.

They would overwhelm any defenses and only a few would need to get through to destroy a tanker.

If multiple tankers are together in a line the risk becomes greater: more targets for the drones to hit and any fires or explosions on one tanker might spread to other tankers.