Because you don’t like to train them.
Because you don’t like to train them or because you don’t know how to train them.
Classically, there has been the idea that the calves (gastrocnemius and soleus) are muscles that respond less well to weight training and therefore are more difficult to grow.
Recently, a study was published showing that it is relatively difficult to grow the calves relative to other muscle groups, because the rates of protein synthesis in these muscles in response to strength training are lower compared to other muscles such as the quadriceps (only a 35% increase in protein synthesis in the calves compared to a 100% increase in the quadriceps).
Therefore, this study supports the idea that it certainly costs more to grow the calves than other muscle groups.
One possible explanation for the low rates of muscle protein synthesis in the twins is their muscle fiber type composition. The soleus muscle (part of this muscle group colloquially called “twins”) has a very high proportion of type 1 fibers (>80%), which have a relatively poorer response to hypertrophy (for a variety of reasons that need not be explained). In contrast, the quadriceps only have approximately ~50% type 1 fibers.
However, the calf muscles also include the gastrocnemius, which has a muscle fiber composition more similar to the quadriceps muscle.
Therefore, the gastrocnemius may respond better to strength training than the soleus.
In addition, this musculature performs high volumes of work because they are very active during the day, which may decrease muscle protein synthesis rates.
Even so, the most important reason why your calves do not grow is in the short and medium response at the beginning, since perhaps the key lies in knowing how to provide the right stimulus knowing their peculiar characteristics at the anatomophysiological level.