Because the throttle linkage can be a safety issue. Check and replace all parts that are excessivly worn. You need the linkage in good reliable condition.

Should be cheap and easy enough to accomplish yourself. Even better parts from a salvage yard may do. The linkage just should not be falling apart.

Vibration over the years takes it's toll is the predominate cause. Combined with owners never cleaning and lubricating the swivels etc.

Also if you have a friend push the throttle pedal to the floor you can examine the lever on the injection pump. Is it being advanced to it's stop? If not acceleration and top end will be comprimised.

This type of issue is very common on the newer 123 cars at least. There I at last got the statement out that the 123s are newer cars.