I can get why some neighbour decorations can be really annoying, but I do like some of the gentle lights (and the delightful giant green pentagram one of the nearby houses has, it is a highlight of my commute this winter) when I'm coming home or out early in the morning for work while it's still do dark. It's even more frustrating that you can't talk to your neighbours about it, and may need to get wider blackout curtains to deal with that.
It's only still christmas for those who observe it as a Christian tradition.
I don't celebrate Christmas at all, but know many places including schools where we're still in the 'Christmas break'.
I blame SM and bloody Americans in general for this idea that lights need to go up on November and come down on boxing day!
Social media and shops eager to move onto the next thing, yes; Americans not so much - it's fairly common in parts of the US for Christmas lights to be up all year, to the point there are country songs that use that as an identity marker (Redneck Woman instantly comes to mind for me).
My understanding is that the 12 days of Christmas has pagan origins
The origins come from a combination of Jewish traditions and early debates and traditions within the Christian churches that grew in various churches based on the dates for Christmas they established after establishing the dates for Easter based on the Jewish calendar for Passover. This was formalised in the 6th century within certain denominations, particularly in parts of Europe where Christianity was well established. The 8th day after Christmas is the Feast of Circumcision, obviously from Jewish traditions, followed by the 12 night for Epiphany as a feast day based on early church decisions around when the Magi arrived and/or when Jesus was baptised, again depending on which church branch.
The coincidence comes from many aspects of the Jewish calendar lining up with the moon, as it's a lunisolar calendar, and certain churches later making administrative choices to line up certain important dates that were set with their local solar calendars instead as they separated out from Judaism. Easter is set after the Vernal Equinox because of Passover, and the rest of the Christian calendar flows from that with different denomination adjusting their calendar to their own liturgy and the calendars they're using.