While there is more confidence now on the security of SHA-2, or rather the lack of transference of the SHA-1 approach to SHA-2, this was not the case in 2005-2006 when NIST decided to hold the SHA-3 competition. See for example the report on Session 4 of the 2005 NIST workshop on hash functions [1].
[1] https://csrc.nist.gov/events/2005/first-cryptographic-hash-w...