The article did mention the cells grow more slowly, maybe this explains why. They framed the impetus for this experiment as being "why do we have so many redund

The article did mention the cells grow more slowly, maybe this explains why. They framed the impetus for this experiment as being "why do we have so many redundancies in codons", maybe the answer is that evolution favored generating new tRNAs for the more used amino acids, speeding up translation? This kind of thing could also be accomplished by changing the rate of generating tRNAs, and for all I know that plays a role too. I'd never really put much thought into why the code was set up that way, its interesting to think about.