There are a lot of factors that affect internet bandwidth (speed). Some main factors are Bandwidth Allocation, Compression and Decompression Technologies and Distribution Method (Broadcast vs Unicast).
Bandwidth: Cable TV has dedicated spectrum to each channel. Overall, the system uses a LOT of spectrum… a range over 600++ MHz (often 54 - 1000 MHz, older systems are usually clean up to 750MHz). Cable plays games, they heavily compress some channels… to fit more digital channels on the same RF spectrum — quality suffers.
Compression and Decompression Technologies: The cable TV platform is engineered as a closed system: they control the compression/decompression (encoding and decoding) of the video signal, generally done in hardware on their provided set top box.
Distribution Method: “Tuning in” on cable is just changing the RF receiver to a new channel (spectrum). “Tuning in” via the Internet requires one to “request” the channel, exchange parameters, the remote end to begin transmission, and the Rx end to buffer and decode, and possibly adjust bit rate. Once live streaming is occurring, both technologies compete well… one could even get better data rates over the Internet (better quality is possible: with the bandwidth)… but changing channels is the slow part. Cable TV is always broadcasting the channels. Internet: you only request what you want, and your stream is unique to you. They scale differently, and there are various designs and methods to optimize both.
There are a lot of factors that affect internet speed. Most cable systems use a common high speed bus (backbone) that is shared among a group of subscribers. When there are few users, the speed, or available bandwidth can be quite high. On the other hand, at peak usage hours, the bandwidth demands can slow the download speed to a crawl. For example, when I used the cable company for my internet connection, I paid for 30 Mbps speed. In the middle of the night, I could actually see the download speed this high, however, at peak hours, my internet speed slowed to less than 1 Mbps. That’s why cable TV is faster than Internet or Internet TV(IPTV).