Supreme Court decision has become final
Because it has not been challenged.
Supreme Court decision says the PM is being sentenced and convicted not only for committing 'contempt' but also for 'ridiculing' the court.
Had it been a case of simple contempt, the speaker had the discretion to declare that the membership of PM does remain un-affected for example on the question of the required quantum of sentence i.e. at least two years.
The speaker or the PP has cleverly or mischievously did not deliberate on the question of ridiculing the court and chose the course which suited them.
Had she deliberated on the question of ridiculing the court, the matter would have definitely gone to the Election Commission.
There is no doubt that such a question was there. Her powers were confined just to see whether a question was there and not to sit as an appellate court on the Supreme Court decision which she did.
As a result, she has breached Article 63(2) and Article 63(1)G of the constitution as well as her oath as the speaker of the National Assembly by allowing an undue favour to a member (the PM) of her party.
Now the situation is, Article 63(1)G has become effective as the decision has not been challenged.
Under this Article, a member of Parliament who has ridiculed the court (or Pakistan Army) has become automatically disqualified.
By not challenging the Supreme Court decision, the PM has not exercised his right of
appeal and has admitted that the charge of ridiculing the court was correct.
As a result a new legal situation has arisen where the speaker decision (not ruling) has become irrelevant and power has moved to the Election Commission to notify that the PM has disqualified automatically as a member of the National Assembly and is not eligible to hold the office of the Prime Minister.
As a question of law, neither the speaker nor the Election Commission can sit as an appellate court to the Supreme Court decision.