Even Kaley Cuoco was against Penny's The Big Bang Theory ending. Uneven storytelling was a recurring problem, especially in the last season of the nerd-centric sitcom. The Big Bang Theory spent too much time on Sheldon and Amy's bid for the Nobel Prize in Physics, but, in an attempt to do something different, it also introduced a marital conflict for the Hofstadters which many felt come out nowhere.
Penny and Leonard were already married for a while by the time The Big Bang Theory began its final season. Despite being the show's primary relationship, many felt the show made their narrative stagnant, effectively forcing them to become supporting characters. To remedy that, the show revealed that the couple had conflicting thoughts about having kids in The Big Bang Theory season 12. The issue was inconsistently tackled and went on odd twists and turns until it was instantaneously resolved when it was revealed that the pair was pregnant. Despite Penny's initial hesitation to have a child, she appeared not to mind the unexpected turn in her life.
Three years since the show ended, Cuoco spoke candidly about Penny's final fate on The Big Bang Theory in the new book, The Big Bang Theory: The Definitive, Inside Story of the Epic Hit Series. She admitted that while it was heartwarming to see the Hofstadters be excited about the impending arrival of their first child, she didn't want her character to be pregnant. Read Cuoco's full quote below:
“I actually wished that they did not [make Penny pregnant], because I loved that message [of Penny not wanting kids] so much. It was cute how the writers did it at the end with Penny’s surprise pregnancy, and all in all I’m glad, but I was actually voting for her not to [get pregnant].”
What Penny’s Big Bang Theory Ending Should Have Been
Ultimately, Penny and Leonard's final The Big Bang Theory ending wasn't all that bad. The premise was interesting, and it could have been a great arc had the show had time to properly executed it. Unfortunately, instead of tackling it with care, it was treated almost like an afterthought. The show dwelled too long on the pair's differences instead of showing that they were actively trying to resolve their issue. Prior to the reveal, there wasn't any indication that Penny was willing to change her stance on the matter, which makes her reaction at the end confusing. Frankly, The Big Bang Theory could have gone either way with the Hofstadters' finale fate if it had a concrete road map to justify its chosen ending.
While The Big Bang Theory ended on a happy note for Penny and Leonard, it's difficult to ignore the possibility that their accidental pregnancy could mean marital problems for them down the road. Young Sheldon has demonstrated the downsides of this matter primarily via George and Mary's rocky marriage. Perhaps CBS can reveal what ultimately happens with the pair via the proposed The Big Bang Theory revival or even through its spin-off prequel.
Source: The Big Bang Theory: The Definitive, Inside Story of the Epic Hit Series