There are 2 main factors.
1) Specification and Options fitted. Some parts are in limited supply as didn't secure enough capacity from suppliers factories. The specs are also different in some countries, so if your country has a part as standard then more likely to be affected.
2) The quota system. Every country and dealer has sales targets for each model, and quotas exist to spread allocation and stop individual dealers ordering lots of production, and thus blocking others. Sales teams rarely tell you, but if they have reached their quota then your order probably won't be accepted by factory until they reach a month with open quota.
The other main factor is iV hybrid models (now withdrawn from sale) are months behind (seems to be nearer 18-24 months)
Leasing firms get their cars supplied through a dealer, and due to squeeze on production capacity, that dealer might only be getting say 2 cars a month, which isn't great if they took 15 lease orders. There are also rumours (not confirmed) that trying to deliver highest spec with most options as these are most profitable cars, which obviously clashes with shortage of expensive option parts. Leased cars are often for businesses so tend to be lower specifications