This was done so that if an archer approaching the tower nocks 5 arrows at the same time, he cannot hit guards in all 5 windows at once.

Later, purposefully-designed bows rendered this defense useless.

Looks like a dynasty of master trolls who were also masons.

But I wonder if there’s a better reason

css is hard

This is a clock tower. Most likely the internal mechanisms for clock precludes a centerline window. Something bolted to the wall, etc.