Hate to deflate the conspiracy theories
But there is no tax or planning advantage to gaining the permission under a different name. Planning permission is given to the site, not the applicant, so if Joe Bloggs made the application then sold the site, the permission is still there and John Smith is free to build the permitted scheme. You don't even need to own a site to apply for planning permission on it, though in england you need their permission. In scotland I could submit an application to build 2 bed maisonette on the top of the scottish parliament and as long as i pay my £150 they'd consider it.
The only control is on the copyright of the design, but that is easily dealt with and wouldn't be a problem in this case.
The reason will either be to hide their plans and make them slightly harder to find for nefarious purposes, or to avoid any "anti-amazon" campaigners hijack the process... or litterally to hide their building layouts, others might seek to copy the arrangement.
alternatively it could well be that a separate development company is buying the sites, putting in the application then selling the lot to amazon.