I'm an ex teacher and on almost all of the school threads I am on the teachers side but in your case I think you are a 100% right.
I always kept records of this stuff, always ensured everyone got it once, and I also always found a reason to give it (never just 'because there was nobody else to pick' - I react hope that wasn't the teachers words!). Sometimes it's hard but often you can engineer it if you have someone in mind that week - even just picking them to help you with jobs and then mentioning how helpful they've been around the classroom etc.
As a child I was constantly overlooked and the same kids got everything (parts in the school play, awards etc.) I always wished I would be noticed. I absolutely loved writing and one year a teacher noticed and gave me lots of encouragement and praise and to this day I remember her comments to me about it and remember finally feeling seen.
There are so many things that are really difficult about being a teacher but making sure each child is noticed and praised is an absolute necessity. I'd honestly put tracking my star of the weeks as more important than tracking their academic progress.
However presumably there's a new teacher this year and so I would tread lightly and not assume they are googling to do the same as last year. Since the term is new it's not unusual yours wouldn't have got SOTW yet.
Personally as a teacher I wouldn't have minded an email about this at all as long as I wasn't being blamed for what previous teachers did and the tone was polite rather than critical. If it were me I would just explain that your son really looks forward to star of the week, never won at all last year and really hopes to win this year and that you think the recognition would really help his self esteem. That you'd really appreciate it if the teacher could keep an eye out for him doing something that would be worthy of SOTW this year. I'd explain you're not asking for him to be given it right now but that you really hope he can get it at some point over the academic year.
Honestly if you sent me that email it would probably be one of the nicest parent emails of the term
Some of the correspondence from parents was so rude and so unbelievably entitled that your email wouldn't even get a quarter or an eye roll.