Window manager blank, why does execution stop at XNextEvent?

I'm attempting to run an older WM using Xlib, the source code is here:

https://github.com/pyknite/catwm/blob/master/catwm.c

setup() seems to run smoothly but the program stops at the while loop in start().

To try and figure out why, I'm using xtrace to intercept the Xnest session that I'm running catwm under but the output isn't giving me any clues that I can make sense of.

These are the last five lines of the xtrace output:

000:<:0030: 16: Request(33): GrabKey owner-events=true(0x01) grab-window=0x00000026 modifiers=Mod1 key=0x18 pointer-mode=Asynchronous(0x01) keyboard-mode=Asynchronous(0x01)
000:<:0031: 16: Request(2): ChangeWindowAttributes window=0x00000026 value-list={event-mask=SubstructureNotify,SubstructureRedirect}
000:<:0032:  8: Request(60): FreeGC gc=0x00200000
000:<:0033:  4: Request(43): GetInputFocus 
000:>:0033:32: Reply to GetInputFocus: revert-to=None(0x00) focus=PointerRoot(0x00000001)

I don't understand how any of this relates to XNextEvent, where the issue seems to be. How can I get the WM to actually work as it's supposed to from here? Thanks