Recurrent viruses on unused user accounts?

Before I ask, here's a little about my OS and other info.:

• Windows 10 Home, v. 1607; 64 bit
• Dell Inspiron 5520 (he's an old man, I know...) w/ an Intel i5-3210M @ 2.50GHz; 6 GB of RAM
• Bitdefender Free Edition, v. 1.0.21.1109; self-updating/scanning
• There are 3 user accounts; only one (mine, obviously) is used and only by me. The people who previously used this laptop are all in the household, but they have their own laptops and apparently have no need to use this one anymore.
• I am not a computer whiz, but I have a generalized knowledge of them. I'm learning more about malware and what they affect because of some "funky" stuff happening for 6+ months... or maybe it's all benign; that's why I'm here.

Alright, so, I've always wondered why only ONE user account on my laptop seems to have recurrent viruses detected and subsequently removed despite, as stated above, no one to my knowledge accesses that particular account anymore. Here's an example of what will be detected as shown in the Bitdefender log:

• FILE NAME -- c:\users\...user.account.in.question...\downloads\setup (16).exe
• INFECTION -- Gen:Variant.Adware.Kazy.372709
• ACTION -- Deleted

And here's the only other thing detected on that particular virus swipe:

• c:\found.000\dir0000.chk\pursuepoint.purbrowse64.exe
• Adware.SwiftBrowse.P
• Deleted

My question is: WHY would a seemingly unused user account frequently (weekly at least; daily at most) hold host to these viruses? They get deleted every time!

On a side note: my disk usage is always at or hovering near 100%. Flash, superfetch/prefetch, BITS, Windows Search, etc. have all been appropriately tended with and the issue persists.

Thanks for any help in advance.