why are sulfonic acids stronger than carboxylic acids

Sulphonic acids have general structure RSO₂OH and carboxylic acids have structure RCOOH.

Strength of an acid depends on its tendency to undergo deprotonation to give the conjugate base of the acid .More stable is the conjugate base which in both of the above cases is a resonance stabilised anion, more will be the acidic stength.

In case of sulphonic acids the anion  formed after deprotonation (RSO₂O-) is more stable due to the resonsnce stabilisation of the anion by dispersal of the negative charge over three oxygen atoms present  as compared to carboxylic acids in which the negative charge in the anion(RCOO-) is dispersed over only two oxygen atoms present.

Hence sulphonic acids are stonger acids than caboxylic acids.