Why is SHA3 prefixed with SHA despite the fact that it is structurally different from SHA2 and SHA1? Why is SHA-3 prefixed with “SHA” despite the fact that it is structurally different from SHA-2 and SHA-1? 

SHA-0, 1 &amp; 2 and MD5 is based on Merkle–Damgård construction, while SHA-3 falls under Sponge functions.

Therefore why SHA-3 is still prefixed with “SHA” despite the fundamental difference in its construction?
SHA3 is the name of the hash function standard, and the acronym is for 'Secure Hash Algorithm', pretty neutral one saying nothing about the structure.  The algorithm itself was originally named Keccak by the developers.  After winning the SHA3 competition, Keccak became SHA3.