In short, because they can ask, because it has always been that way, and because everyone else does it.
Originally, this was needed before the popularity of internet when official communications were sent via mail. This is so they can send interview schedules and offers.
In modern times, no one needs it for an applicant. The reason that it is still there is because there has been no demand to change the process. Hiring managers do not have the time; HR figures more data the better and why break something that still works; HRIS needs to make hiring process busy and complex to sell the need to HR departments.
Companies are hoarders like people. Companies believe they can re-use the information for future sourcing. In reality, they never do. It is easier for them to post onto a job board and get all fresh data. With the lack of demand from applicants to demand this change, there is no reason for companies to stop this practice.
Address may eventually be needed for background check, official job offer, etc. This can always be requested later. Most companies use third-party so in most cases, the applicant has to provide the address again anyways. Also when you join the company, you will likely have to provide the address yet again for tax purposes.
Do they need it? No. Does it hurt to ask it? No. Applicants can change it, but that will unlikely happen as time has shown.
I understand this is an old post. Since it came up first on my search, I hope this may help.