Alex Kulak2 said: "Why wouldn't Stoppard be writing the adaptation himself? No disrespect to Marber, he's a great writer too, but Stoppard's an Oscar-winning screenwriter who's adapted his own material before, and even worked with Spielberg before (he was a script doctor for the 3rd Indiana Jones movie)."
Maybe it is as simple as he does not want to, nor does he need to! He is, after all, 85 years old, and based on what I've read, if he is going to tackle another project at this point in his life, it seems he would rather it be another play. He told Maureen Dowd in the NYT last year "that he did not want to work on any more movies 'because I’m a playwright, and if I have a play to write, that’s all I want to do.'"
I would imagine if he does not want to work in movies, that goes double for television - a limited series to boot - it would be quite time-consuming and for what? Sir Tom likely said all he wanted to say about Jewish identity and the Holocaust within the neat confines of the play and thus happy to hand it over Marber. Though the play was greatly impacted by Stoppard's coming to terms with his own Jewish identity, it is not based specifically on his own family and, as such, probably easier for him to turn this over to others. He is likely confident Marber will not bastardize his blueprint.
As Stoppard is, to many, the world's greatest living playwright (English language), with an Oscar, as well as a raft of Tonys, Olivers and BAFTAs on his shelf, I doubt he needs or covets a (yawn) Emmy that his television authorship might yield (that being said he should have won several years ago for PARADE'S END - losing to BEYOND THE CANDELABRA). He'll probably get a producer credit so if the production distinguishes itself, he can always collect one that way with no heavy lifting required.
Lastly, doesn't need the money, for sure.
I am one of those who was (perhaps in the minority) terribly disappointed in LEOPOLDSTADT. Despite some intelligent dialogue, beautiful staging by Marber and some lovely performances, for me, it was a bit staid, ordinary and obvious (thematically and narratively) - and mostly, sadly, so non-Stoppardian-- no better than an above average special event network television movie circa 1970's. Given Stoppard self-reproach for not knowing more about his past, if he was going to do an assimilated family-faces-the-Holocaust story, I expected something a little more skewed and challenging (other than keeping the characters straight). It only really began to grab me in the last act. Since he took the more conventional, sprawling family history approach, a limited television series is probably where this should have landed originally. It might benefit by Marber's further development, but it seems likely to lean even more heavily into the traditional narrative and though it likely it will be smart, I feel I will still be disappointed.