It's because you need to see repeated addition as multiplication.

2^5 + 2^5 is the same as "2 lots of 2^5".

2(2^5) = (2^1)(2^5) = 2^(1 + 5) = 2^6.

For the second, you have 3^5 + 3^5 + 3^5, in other words "3 lots of 3^5".

3(3^5) = (3^1)(3^5) = 3^(1 + 5) = 3^6.