Probably because the UK isn't a particularly large country (or group of countries). No matter where you are in the UK, you are never more than 150 miles from the sea - which may account for the rivers being relatively small. rivers such as the Nile or Amazon have travelled thousands of miles from their source to the sea.
There are 32 rivers in the UK! including the Thames and Trent which is the largest in England
Small creeks, streams and rivers that flow into larger rivers are called tributaries
The UK is one of the best places to go Chub fishing. They are very abundant in many small rivers and make a great catch. Faster flowing small river tributaries of larger rivers make the best locations.
The Clyde, the Severn and the Avon are but three of the rivers in the UK.
rivers
There are hundreds of rivers in the uk, the best known is probably the Thames.
Rivers are coloured blue on most UK maps
The rivers Severn, Thames, Trent and Great Ouse.
Tributaries.
There are many rivers in the UK, here are just a few of the larger ones, The River Severn, The Thames, The Mersey, The Tyne, The Clyde, The Trent.
Clyce
Thames