A streamer with a powerful gaming PC can still be limited to a soft, blocky picture by the connection leaving their house. In the United States that limit comes from how residential internet is provisioned rather than from the equipment.
Residential service is deliberately asymmetric
Most American cable connections allocate far more capacity to downloading than to uploading, because typical household use is overwhelmingly inbound: video, browsing and game downloads.
Advertised speeds emphasize that download figure, and the upload number appears in smaller print or not at all. A subscriber comparing plans is comparing the wrong half for streaming purposes.
Fiber service is generally symmetric and removes the constraint entirely, which is why availability of fiber at a specific address determines what that household can broadcast.
Bitrate is the quality decision
A stream is compressed to a target bitrate, and that number controls how much detail survives. Fast motion, particle effects and foliage all demand more data to stay clean.
Setting a bitrate above what the upload path can sustain does not produce a better picture. It produces dropped frames, because the encoder is generating more data than the connection can carry.
Streamers therefore choose a bitrate below their measured sustained upload rather than their peak, leaving headroom for everything else the household is doing.
The connection is shared with the game itself
An online game is also sending data upstream continuously, and its packets are small, frequent and extremely sensitive to delay.
A saturated upload path delays those packets, so a streamer who pushes bitrate too high degrades their own gameplay while degrading the stream.
This is the mechanism behind the common complaint of feeling worse in a game while live, and it is a bandwidth conflict rather than nerves.
Cable capacity is shared with the neighborhood
Cable systems share upstream capacity among the homes on a segment, so a subscriber's effective upload varies with what neighbors are doing at that hour.
American evening peak is exactly when most streaming happens, which means the constraint tightens at the least convenient time.
A streamer testing their connection in the afternoon can therefore configure a bitrate that fails reliably every night without any change to their setup.
Data caps convert quality into a bill
Some American providers apply monthly data allowances that count uploaded traffic, and a streamer running long sessions generates a substantial volume of it.
Exceeding an allowance triggers overage charges or a slower tier, which turns a quality setting into a recurring cost decision.
Streamers on capped plans often run lower bitrates than their line supports for exactly this reason, and the visible result looks like a technical limitation rather than a billing one.