The things that all these companies list as unlimited do not have limits on them directly.
The limits on the account use are elsewhere than the ones that the marketing team advertise as unlimited.
BlueHost actually refused to list anything as unlimited for a while and found that they were falling behind because everyone else that they were competing with advertised unlimited space and bandwidth.
As a couple of examples of how it is actually impossible for anyone to make use of any of the unlimited space offers - ALL of those offering unlimited space specify that the space MUST be used for hosting web pages so you can't use the space for anything apart from web pages. Since web pages themselves are relatively small the only sites where any significant amount of space would be used would be those where files are being offered for download. Even a site with thousands of web pages and a couple of hundred pages offering files for download is only going to use a few Gb of space at most. Plus working full time on writing web pages it would still take you years to create thousands of pages.
Also many of the hosting providers place a limit on the number of files you can have rather than the space the files can use. This makes sense because the disk storage is cheap so that taking up extra space isn't going to cost the provider anything much at all while having too many files can significantly impact on recovery times if the server goes down and the other accounts sharing the server will not appreciate it if it takes a week to bring back up because one account has millions of files to verify.
All web hosting has limits. When they advertise something as unlimited it means that they don't need to limit that because the things they do limit impose reasonable restrictions on it without their needing to limit it directly.
With web space I'd be surprised if any of the shared hosting providers offering unlimited space could be used to host over 500Gb of files as I expect that the limits that they impose would make it impossible to get anywhere near that total file size while remaining within the limits that do apply. Most accounts would probably be under 1Gb.
BlueHost/HostMonster/FastDomain (which are all the same hosting but with different branding) are actually the biggest shared hosting provider with almost two million accounts on their servers.