I’m the same as you, it’s hard to invest myself in something that might never conclude. I also forget a ton of shit if I have to wait 5+ years between books.

My only exception if the series isn’t finished but the author has very consistent output, ex: every 2-3 years we get a book. That said, I might have to abandon this rule because I was knee deep in an unfinished sci fi series and, even though the author was very consistent in releasing books, he tragically passed away.