Why do mods nerf instead of buff?

Over the years, people have had issues with mods buffing, and nerfing, certain plants. Winter Melon, Primal Potato Mine and others are key examples here, and people tend to really not like this. There are good reasons that people do this, though, and I think it is important to clarify here. Just look forward to it.
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Core A Gaming's Analysis:    • Analysis: Why We Should Buff More Tha...  
Endless Zone Video:    • The problem with endless in PvZ 2 Ref...  

Timestamps:
0:00 - Intro
1:38 - "You should buff more than you nerf"
6:02 - Why nerfing Winter is good, actually
8:49 - If everything is OP, the zombies aren't
12:31 - Miscallaneous Issues.=
14:59 - Conclusions

Footage is from:
Plants VS Zombies 2
Insaniquarium
Potion Craft: Alchemist Simulator
Bug Fables

Mods used (in no particular order):
AltverZ
Eclise Alpha
Reflourished

Music used (in order of appearance):
Spaces Between - OMORI
Dave's Theme (unnamed) - PVZ2
Decisive Battle - Hollow Knight
Neon Mixtape Tour Choose Your Seeds - PVZ2
Ancient Egypt Wave 1 - PVZ2
Loonboon - PVZ1
Zen Garden - PVZ1

Outro is an original track.