Because software developers selling software are (1) incentivized to offer lots of features, because different individuals and businesses have different needs,

Because software developers selling software are (1) incentivized to offer lots of features, because different individuals and businesses have different needs, but also (2) not very strongly incentivized to either (a) make the program particularly easy to use/integrating those features well with each other (which is one thing you might be thinking of when you say "bloatware") or (b) make the program particularly performant (which is another thing you might be thinking of). Open-source tools, while they might not always limit feature scope (e.g. Blender, Firefox, Emacs, Audacity, Krita) (although this isn't necessarily a bad thing), seem to be better at delivering good performance even for applications with larger feature-sets, partially because their developers are incentivized to optimize for performance due to their own pride.