I’m a bit confused by this. There is an offer for Ultimate for $1, but this message comes up. Why would my gold subscription end 45 days early when I upgrade to ultimate just for a month? Am I understanding it right?

I’m a bit confused by this. There is an offer for Ultimate for $1, but this message comes up. Why would my gold subscription end 45 days early when I upgrade to ultimate just for a month? Am I understanding it right?