Carrier and bandwidth?

why when carrier increase bandwidth increases?

Because of more availability of the carrier bandwidth in the higher band. For example in GSM 900 total BW is 915-890=25 MHz only however for GSM 1800 it is 70 MHz.

For LTE please refer to 36.104 chapter-5
And for 5G refer to 38.104 chapter-5

For the detailed bands and bandwidth available.