If everyone who got on the escalator stayed in their position on the escalator until they got off, this would mitigate bunching at the top. But practically, when people get on the escalator, many people walk (while other people just stand) which can throw off the rate that people arrive at the end of the escalator. If two people get on an escalator 3 seconds apart, but then one of them moves forward on the escalator so that they are both on the same step, then they would exit the escalator at the same time rather than 3 seconds apart.

Additionally, the people getting on the upwards escalator, at, for example, Floor 1 aren't the only people that will be getting on the upwards escalator on Floor 2. There will be other people from Floor 2 that want to go upwards as well.

The design should also account for unusual situations as well. Just because someone got on the first escalator with no problem doesn't mean they won't accidentally trip or fall when trying to get on the second escalator. And if that happens, you don't want people getting hurt just because a sudden traffic jam caused a huge bunch of people on the landing between the escalators.

I was curious so I did some additional reading. Based on promo material from escalator manufacturers [1], there is mention of safety issues regarding the amount of space on escalator landings, but there is also a lot of talk about optimizing traffic flow through product display areas. My guess is that the mall's decision to place the escalators the way they did is primarily driven by that, but as someone who used to work in a building where the exit to one escalator was directly next to the entrance to the next escalator, and personally witnessed huge traffic jams (and had the awful experience of being uncontrollably pushed towards such a jam by an escalator), I do appreciate the design for safety reasons as well.

1 (PDF WARNING): https://www.schindler.com/content/in/internet/en/mobility-so...