why i don't get anymore halfblood experience points if i always play by these cards ??

After reaching certain reputation levels certain cards wont provide reputation anymore and when you get very close to level 50 reputation you will need use reputation crests to finish it off, you can get these crests from spending tower tokens on them. If you click into your Halfbloods reputation section under the current reputation points bar it will show tips of what things can still provide you with the selected reputation type.