I get a pound of ad flyers twice a week. I do my best to separate them from the real mail, but it's not unimaginable to dump a letter or two into the recycle bin along with all that paper waste.
Also people move, and mail gets misdelivered sometimes. I guess it's possible to convict and jail someone for ignoring summons, but the evidence should be fairly convincing - such as failing to respond to several summons while still paying your regular bills. Such selectivity would be hard to explain.
It all depends on the judge’s mood. Most likely they just fine or warn people but I did read on the local boards that a few were sent to jail recently after a bunch of summons were ignored. They had to set an example.