SCUBA is
not only an infiltration technique.
SCUBA (air, O2, mixed gas) is an
additional skill which has many other applications.
Commitments of the limited dedicated UWO assets at any given time - combined with time, distance, transportation, weather, mission constraints - provide the arguments for having UWO qualified personnel/teams available in-theater when and wherever necessary.
USN - like the USAF - provide transportation for SO teams as directed by JCS. We used PBRs, CRCs, subs (SS and SSN/SSBN) and SDVs - along with other surface craft and USN RWAC. A taxi is a taxi no matter who's driving the damn thing.
PJ SCUBA training - unless they later manage a slot to the CDQC - is a basic introductory diving course at Panama City and nothing like the CDQC.
CD qualification is a time intensive and expensive skill to attain and maintain, and not everyone has the aptitude for it.
Putting one's proverbial eggs in a single basket makes no sense - especially within the SO community.
Richard's $.02