I wonder why only black people are called slaves & only white people were called slavers, considering that most Europeans were under the yoke (as in slavery) & most slave sellers in Africa were black ?

Indyvidual,

There were twice as many whites sold into slavery by the Barbary pirates as were sold into slavery in North America.

One of the causes of the collapse of Rome was the trepidation on the
Roman trading ships by Barbary Coast Arab slave traders.
This forced Rome to use much more expensive land transport.
It is thought that more than 1 million Europeans were taken by the slavers.
The Slav countries were the major source of slaves, hence the name.
Now they have come for Europe itself !
The Arab slavers actually raided Iceland looking for blondes.
Blondes got much higher prices !
I would bet they still do.