For comparison, BMW's models (electric and ICE) offer more paint options, more wheel options, 4x as many interior color/upholstery options, 6 interior trim options, and multiple add-on packages.
Yes, it takes longer, because when you customize your BMW (or any other non-Tesla automaker's cars) you can actually customize it to your preferences, and the customized interior is what can take a few months because BMW (or whichever automaker you went with) is actually building your car based on your customizations, and if you select an uncommon interior/trim/package combination, it can take some time to get to the front of the queue.
You get your Tesla in a week because you're not actually customizing anything. You're just getting whatever Tesla already built.
And if you want a non-customized car and getting it quickly is a priority, you can just go to your nearest car dealership and get a new car in an hour, and whatever that new car is will have better build quality and range then your Tesla. And with Tesla's recent price cuts killing the used Tesla market, your non-Tesla will also have better resale value when it comes time for your next car.