A switchable 50 Ohm termination,is in my opinion,a bit of a gimmick,although some people are very taken with them.
Most older Oscilloscopes don't have them.
Unfortunately you can't just stick a toggle switch & a resistor across the input,as a switched termination needs a bit of finesse in design at high frequencies.
Special switches must be designed,or relays used,all of which adds mechanical complexity & creates possible reliability issues.
A fixed 50 Ohm termination would severely limit the versatility of your 'scope.
Through terminators are available for both 50 & 75 Ohms,which are,again in my opinion,a more versatile way of using a terminated input.
The external terminations usually have a higher power rating,but if you do cook one,you don't have to replace any bits in your 'scope.