I can't see how, even in hard fishing, that wire loop would open up and allow for the spinner to come off. Some of you guys must use brain like rope and poles like tree stumps and give a cast like a Roland Martin on steroids to loose spinners.
Many commercially made spinnerbaits only have a looped wire, looks like a tear drop, and I've had swivels & blades come off with them. IMO, that's done intentionally, as it takes less time & effort to make them, but also it's "planned obsolescence", knowing the spinnerbait either has to be repaired or replaced. I don't think that way, and I'm sure many custom lure makers here don't either. I've always wanted lures to last, whether for my own use, or if I'm selling them to someone else and a reason I started making my own.
I have a couple of purchased spinnerbaits with the wire bent as Lamar suggested, but never saw a need to do it, since I've never lost a swivel & blade on those I've made.
How I form the loops, is no different than some are doing with bladed jigs when using a wire form for the line tie, except some of the wires for spinnerbaits are lighter. The one in this photo I think was .045 wire, which isn't going to open easily, and I used the heavier wire since I'll use it for Striped Bass. I've done this with wires from .029 to .051 diameter.
These loops are also only about 3-4mm diameter and it would take a good bit of effort to open them. If cutting the wire as I do with hand cutters, it leaves an end that isn't flat, and some may bend the wire without filing or grinding that end flat. IMO, that's part of why I've never lost a blade. The extra effort for these small details make a big difference.
I'm not knocking what Lamar suggested either, that certainly assures a swivel & blade can't come off, but how I've been making them has worked too.