The practicalities of it aren't as easy as that, sadly.
The stadium has to be mapped out as to where people should be sitting (we know it won't be adhered to on the day but we can't plan for that). The distance between people, numbers in certain rows etc - all of that has to be scrapped and started again with any change that's implemented. If the attendance number has changed, that's going to have a big effect.
Our list of season ticket holders isn't just individuals, there's family and social groups to consider, so trying to get the numbers right isn't as easy as just putting everyone into a pot and drawing them out.
There's no doubt the ticket office or whatever department is in control of this have had some challenges this summer and haven't always found it easy, but in this case the club are trying to get as many fans as possible into the game and that sadly means a bit of work and time. They won't want the sort of difficulties that happened with the friendlies. It probably means the ballot is delayed a little, which is unfortunate and I do understand the frustrations and problems that causes for many fans.
But I think it's unfair to criticise the club for trying to get as many fans back into the stadium as possible, and I don't believe this whole process is anywhere near simple.