Bootcamps are just too short. I think the sweet spot for a coursework in programming is a year to two years. That's essentially how long my university degree was if you remove the non-CS required classes.
The ones that are only a month long...well it's a nice introduction to coding I suppose, but I can't see it as much more than that. There's definitely a "too short" but it depends on a lot of factors as for where that line will be.