Cause it's "redline" fuel cleaner. You need to be at redline.
So, please forgive me if I've missed that this is meant sarcastically or a case of 'pulling my leg'!
BUT
Anyone stupid enough to run their vehicle/engine at redline for an hour just to clean their injectors deserves everything that's coming to them!
And the fact that Tik-Tok said he is going to sit in 4th gear on the highway for an hour is also 'very suspect'.
If the thought process is you want your injectors to be fully open for an hour for your cleaner to work, I'd suggest buying a different cleaner!
If however this is just banter, being stupid or whatever else, just ignore the stupid Limey and carry on with your day
Oh, and could you add sarcastic smileys after the sarcasm