If your suggesting infernos should be available at all TH levels, "Haven't you ever attacked at TH2,3,4,5,6,7,8,9 or did you just upgrade troops at TH10 and started attacking ONLY TH10s?!?! For the love of crackers, how will a Giant with CC Healer attack survive at TH4 if the opponent has Single Target infernos.
Also, the cost of inferno is 5,000,000 and the maximum storage capacity at TH4(Just an example) is 500,000. How in the world are they gonna build it?!?!