Huh, really? Most of the people I know who tie-in with the figure-8 use the standard overhand safety knot (or they pull the tail back through the bottom loop of the eight). Most of us have been climbing for decades. I guess old habits die hard?
maybe excessively long tails are a better sign…
Even my dog gets away from a bowline with a minimum of moving around the front yard.
ETA: The last person I saw tie-in with a single bowline was Christian Griffith (of Verve fame) using it to tie-back in after cleaning the anchors of a warm-up in the Ruckman Cave at Rifle Mountain Park. He also didn't secure the rope whe he untied to thread the anchors, choosing instead to just step on it. Not exactly a great example of anchor safety...
The balancing act the gyms, in particular, are trying to play is that knots should be both secure and easily verifiable on sight by gym staff, more or less entirely for liability reasons. A yosemite finish, or a bowline, are both dead-ass safe and in some cases better than a traced eight, but they're harder to glance at and know they're safe. That's totally fine at the crag, but it's a liability issue at the gym.
About 5-6 years ago the gyms became much more honest in their instruction for new climbers, and will now actually say the quiet part out loud, which is that a backup knot is really there to 1. ensure that new climbers leave enough of a tail on the figure 8 and 2. are a way to prevent that probably extremely conservative tail from whacking you in the balls when you take a whipper.
sport gyms absolutely do not like people who insist on tying in with a bowline.