That's not the intent. But de facto, they either have no or that effect. Particularly in primaries.

There is also a huge messaging difference between casting a blank ballot and not showing up at all. The presumption is you can safely ignore someone who doesn't vote for several cycles because they tend to keep not voting for novel–but consistently exculpatory–excuses each time around. You have to still pay attention to intermittent voters if you don't want to get caught wrong-footed by a wave.