Withdrew after round three and told them the actual reason instead of inventing one

Four rounds agreed upfront. After the third they added a "culture conversation" and a case study presentation, both unpaid, both on weekday evenings.

I emailed and said plainly that the process had outgrown what I could give while working full time, and that I'd have stayed in it if the scope had been set at the start.

The recruiter replied within an hour thanking me and saying she'd been raising the same thing internally. Nothing came of it, no magical re-invite. But I'd been carrying this idea that withdrawing torches the relationship and it just didn't. Turns out you can say the real thing politely.