It is because of Alonso much more experience compared to Stroll,have you seen the overtake of Alonso to Hamilton in the first race,that as the commentator of the race in Sky Sports said,it has years in the making as a move.Stroll is a young driver relatively and has time to improve,he should learn from Alonso big experience.I think though that in this second race it was an error from the team that they called him early in the pits and he lost his position to both Ferraris before he had a problem with the engine and was told to stop the car.
I know, as I said Alonso is much better driver there is absolutely no doubt about that, nobody ever questions it. But Alonso is 40+ years old and Stroll is just 24 years old, which means differences in reflexes and considering that they are both using the best car aside from Red Bull, Stroll has to do better.
Not like anything would change, father Stroll took the team just so his son can race there, which means that Stroll could be 20th and he would still be keeping his job without a doubt, there is absolutely no reason to be worried about his position. But I just feel bad for him, because he is good enough to do a bit better, he should push himself further, take risks, otherwise it will be a disappointing season and I do not think that they will ever be this good again.