I always found the shuttle "single attempt" landing as not cautious at all. What if anything go wrong? Do you just crash and kill all crew on board?
Well, I'm comparing apples to oranges actually. See Spacex booster landing is quite hit and miss also, actually.
Sorry, forget what I was saying, it's just the wrong things to compare :)
It's true that SpaceX's booster landings are fairly unreliable, but they don't have to be reliable. They make a bit of a mess when they go kerplooie, but it's no big deal. Lives aren't at risk, and the equipment is cheap enough to lose.
The launch was a much better example of brittleness in the Shuttle system. The solid rocket boosters couldn't be shut off or ejected once they lit, so that was about two minutes where there were no options if anything went wrong. Even after booster separation, the abort modes were so difficult that NASA refused to ever test them. The first Shuttle commander said that a return to launch site abort would require "six miracles followed by an act of God" to pull off.
Every other manned spacecraft has the capability of aborting a launch at least semi-reliably, and proves it with testing.
Plus within the next year they are basically going to stop producing new cores, so loosing one won't be "cheap"
The genius of SpaceX's approach is that they built a landing system where it's OK to be unreliable for a while. Instead of being a billion-dollar item like the Space Shuttles were, the Falcon 9 boosters are a few tens of millions of dollars apiece, and the launches are priced to cover the entire cost of them plus more.
ASDS repair depends on the nature of the failure. When a low-margin GTO mission miscalculates and craters, that does indeed take some fixing. A JASON-style tip over and kaboom seems to basically involve picking up the pieces and repainting the lines.
I think your last sentence reverses cause and effect. If they substantially cut down on core construction, that will be because the landings became reliable enough for that to happen. That doesn't make failures costly now.
I will also note that their landing approach is inherently unreliable to a degree, because there's little redundancy. If Falcon 9 loses an engine on the way up, it's fine. If it loses an engine during the landing burn, it's going to kerplode. If it loses an engine on the way up, then that will likely wreck the fuel margin needed for landing. I'd be shocked if Falcon 9 can ever achieve anything like the Shuttle's perfect 133 out of 133 landing record. (I'm not counting Columbia since it was ultimately a launch accident that manifested on reentry, and never got anywhere near the actual landing.) But that's fine, they don't need to.
For booster landings it's probably okay to be unreliable forever as long as the failure rate is estimated properly and the value of recovered boosters exceeds the cost of developing and maintaining recovery capability. Since there are no people or cargo involved it's a straight exercise in accounting.
In cases where they are using three engines during the landing burn, losing one would be catastrophic. You'd lose a third of the thrust you were counting on, and the remaining thrust would be highly asymmetric. The other outboard engine can't gimbal far enough to keep the thrust vector through the center of mass of the rocket.
Well the shuttle is a big heavy glider with little wings. One try, and down from 30,000 feet to ground in 3 minutes. Not problematic, but very special.
The upcoming Echostar 23 mission is flying in expendable mode (no landing attempt) because the mission parameters simply don't allow for a landing. They could try and fail, but they don't really need more data points - especially when people don't realize that these experimental landings are just experimental, and it winds up with bad press.
spacex does walk a fine line between "rapid development causing potential issues" (see AMOS-6) and "abundance of caution" (see CRS-10 delay on saturday)