Can someone explain me, why this show is not weekly reagular?
Many reasons.
1. Something else big is on(sports, award shows, etc), don't want to compete so they show a repeat.
2. Sometimes they just want episodes to air during sweeps so they bump episodes around instead of just 1 huge gap.*
3. Summer and the weeks around Christmas and New Years are deadzones so they don't air then.
*They think thats better like they are keeping it fresh in people's minds.
What it actually does is just cause confusion because an average person isn't going to follow the week here, 3 weeks there and 1 more here.
CBS is pretty bad about it but Once Upon a Time on ABC was like the worst I had ever seen.
3 week break, episode, 2 week break, episode, 1 week break, 2 episodes, 2 week break.