Standard parts are available right away, only not-so-common parts have long leadtimes.
You CAN buy most right away for double the price, if you like.
It's the same for all companies, they all have to plan ahead like that.
Of course, something like Apple is different. If they want to buy billions of part from you but only if they are available within a certain time frame, you'd try everything to make that happen - even giving smaller companies longer lead times if need be.