Because you have little control of things on Home, so good luck tweaking out, and having those tweaks last after each forced update too. Some options have been removed from Pro too (and others only ever existed on Enterprise), but there's still quite a hefty difference.
But, of course, Win 10 is dreadful due to this taking away of control from the user either way you go about it. Dread the prospect of next year myself, as 10 is not an option.

Edit: Specifically, if you do go with 10 (*shudder*), you'll want Pro for some control of updates (still intolerably little, but way more than Home) and group policy (which may be presented as a business feature, but ends up being necessary just for those tweaks you want to do). Bitlocker for encryption (now that they apparently made it work on single files too, not just whole drives anymore) and Hyper-V for VMs may also be handy if you think you may use those.
I'd second that combo, Samsung for SSD and WD Black for HDD. A tad hard to justify the Pro now though, since they reduced the warranty for it to 5 years, same as the Evo. Used to be 10 in previous series. Still has more writes though, and either way the values are past what you'd normally use. And that test that was linked to, from back in 2013 too, shows how much further than the rated values they can go anyway.
Damn, reaching into the PBs, and even the first to fail going several times above the rated limit! That's insane. But yeah, it confirms the sudden death thing, which HDDs don't typically have.
Well, I'm not dt, but no.
For one, the idea is that SSDs (or anything using flash) can't overwrite a sector as a HDD can, but must first erase it. So when you delete something off a HDD what happens is just that the entry in the allocation table gets erased, but the data remains there until those sectors are written with something else (hence the easy recovery too). A SSD will also do that at first, but if the data remains written when those sectors will need to be written again, the write operation will be twice as slow, since it'd need to first erase the old data and then write the new. So you have the trim function, which if enabled (and it normally is) will tell the SSD which sectors are no longer considered in use and it'll erase them when it's not otherwise busy. So, whenever it happens, either when the sector needs to be written again or as part of this maintenance work, that erasure counts as writing, doubling the amount actually written on the disk.
Also, when sectors will trigger wear leveling warnings, after a certain number of writes (again, that means a LONG time under regular usage scenarios), that data will likely be moved to "fresher" sectors, again adding to writes without you actually writing to the disk, this being done internally by SSD, without the user (or the OS for that matter) noticing the difference, assuming it doesn't fail in the process.

Oh, PS, another difference between SSDs and HDDs: SSDs have firmware. Firmware has updates. Not required to install them of course, but some may correct bugs or what not. Updating a SSDs firmware will normally wipe it (or even if you try not to, if possible, there's no guarantee there won't be data loss), hence SSDs come with utilities to make image backups and restore them after such an update. Normally it should be hassle-free, just have the space on another drive to store that image and it'll be put back as if nothing happened. But, of course, scary prospect. I haven't updated mine's firmware for one, and I don't even have the OS on it (was purchased quite recently).