[inglor_cz]

Falcon 9 engines (Merlins) cannot throttle down, they either run on max power or they don't. Which means that any attempts to land are incredibly risky. You have to reignite them at the precise moment to slow down the rocket to zero at the height of the landing platform, or else. That is why the maneuver is called "suicide burn", and it is incredible that someone actually perfected something as crazy as this. The landing legs can absorb a tiny error, but anything over that = Rapid Unscheduled Disassembly (Monty Python theme starts to play in the background...)

Raptors are much more finely controllable and both stages of Starship can even hover when necessary, so the total control envelope, while not perfect, is much larger. That is why they can even try to land into a steely embrace, with no landing legs used.

[wat10000]

Merlin and Raptor can both throttle to about 40%. The difference is that Super Heavy has way more engines, so 40% of one engine is a lot less thrust relative to the mass of the nearly empty booster.

Did the suicide burn actually play a role in the various barge-holing events? It’s been a while but I don’t remember that being the hard part.

[inglor_cz]

I was mistaken, Merlins can indeed throttle down. Thanks for correction.

What they cannot is achieve thrust-to-weight ratio of <= 1 when the first stage is empty, so controlled descent is basically impossible and suicide burn is the only option to land.

When it comes to failed returns, I think that at least once they ran out of fuel several meters early(?)