All these SN-flights...seems that Raptor and the surrounding system is still in development and is pretty unreliable. So why go through all the trouble of flying until the Raptors are more mature?
The Raptor engines themselves work fine on the test stand.
The current challenge SpaceX is facing seems to be in getting the fuel tankage and pressurization system to work properly in the dynamic environment of the Starship's terminal flip maneuver. I can't think of a way to realistically test that non-destructively without building a gigantic rig that physically secures and tilts a Starship, and that probably would cost at least as much as building a couple of additional Starships, and wouldn't tell them if the rest of the system works.
A traditional space program would spend a lot of time and money would to make sure that as far as possible, a test flight would work as planned and an expensive prototype wouldn’t be lost. SpaceX doesn’t work like that. Although they undoubtedly do a lot of prior simulation work, they are prepared to fly at a much earlier stage in the design and build the prototypes as cheaply as possible in the expectation that many will be lost. Early Starship flights are in fact more experiments than test flights.
The traditional development approach is “failure is not an option”. The SpaceX approach is “if it’s not failing, you’re not pushing hard enough” or move quickly and break things to find out what the problem is, don’t study the problem theoretically for too long. The only mistakes that are failures are the ones where nothing is learned and SpaceX monitor what happens with their prototypes very closely.
Sometimes it pays to test multiple things in one go for example Starship prototype SN8 was considered a great success because everything worked except the final landing. Any number of other problems could have emerged concerning the stability of the control system during descent or the ability to manage the throttling and shut down of engines or many other things. But they all worked or at least worked well enough so they get a tick in the box all at once.
Raptor is "good enough" to fly as far as SpaceX is concerned and Elon Musk is also in a very great hurry to get to Mars and is not worried about breaking things or spending money to do so.
Let me counter with a question: why would they not?
What else would they do with the 12 Starships and 60 Raptors do that they have already built, if they're not flying them? Hang them on the wall and admire them?
If you have the vehicles and the engines, why would you just build them to scrap them?