Here's why..... The pros use poly and it may be a better string but the pros have virtually nothing on common with a club player. The pros will use poly for one set or a match and then cut the strings out......why? Because the fact is that after just one match Polys play completely differently . They are not meant to stay in your racquet for am extended period of time. On the other hand Kevlar holds its tension and plays the same much longer. For example a club player who plays with a poly string job for a month versus a Kevlar string job for a month will have a completely different experience. The poly will be dead and lifeless while the Kevlar will play the same throughout. ****Obviously not a full bed of of kevlar !!!! Kevlar must be mixed with gut or a soft string !!!!