Why should I credit to SQ?
 

Recently relocated out of Singapore and back to US. Business travel needs involve very frequent flts on SQ to Asia and India, however, rewards flights are entirely US-Europe on LH and within US on UA. Is this any drawback to deciding to no longer credit miles for business travel on SQ and instead credit SQ flights to UA? Reward bookings using SQ miles for LH flights to Europe are approx 500 US roundtrip vs booking using UA miles earned from SQ flights would not have the rediculously high fuel surcharges. I asked SQ agent to give me reasons I should continue to maintain my KrisFlyer account and he had none to give.

The only reason to credit to KF over UA is to redeem for SQ flights.

Though note that your UA tickets will accrue to MileagePlus based on price rather than mileage.

If USA is home for good UA in the long term could/will be better.
If long haul awards are the objective no sense in paying high cash $$$ award surcharges
A very simplistic measure is how many paid flights on USA-Asia route to get a USA-Eu flight as an award. And then take into account cash surcharges.
AwardAce SEA CDG example

Will be easier to get ff miles from non flying activities to a USA based ffp when you live is USA.
You will not get USA domestic upgrades as an SQ ff.

The UA MP page for SQ flights seems to say the opposite for tickets bought from SQ and credited to UA:

"Otherwise, you should reference the "Ticket number does not start with 016" section.footnote4 You'll earn miles based on flight distancefootnote5 and the purchased fare class and/or fare class flown.footnote2"

Sorry, that comment is incorrect in any relevant context.

If the flight is ticketed by UA, it will accrue to MP based on spend.

If the flight is operated by UA, it will accrue to MP based on spend.

If the flight is ticketed by SQ and operated by SQ, it is neither a UA flight nor a UA ticket, and thus irrelevant to this discussion.

Use Krisflyer if you want to redeem premium seats on SQ as that and having a credit card crediting Krisflyer miles is the only advantage.