You obviously didn't give any answer to US arms embargo in 2008.
Anyhow,
I dunno you have ever read a book called "The confession of the economic hitman" or "The Pinochet files". It might shed some light on the US foreign policy on countries like us.
JR was the US ally AFAIK, Premadasa was not went the far JR had gone. However democratically elected politicians don't help the US foreign policy when their time in the power is limited to 5 years generally. Moreover there is no guarantee for the US that the next government would continue the policies what people like JR had created. There fore US need a enclave where there is no bi polar political parties. That is the reason they try to create enclaves of countries which have predominantly unitary ambitions which could be easily manipulated.
Eelam does not need to be ruled by a dictatorship to be an effective proxy against both Sri Lanka and India. A democratic parliament in Eelam can also work just as fine for US ambitions. That's because there is a fear factor. It's as same as what we see in Israel and Pakistani politics.
West Wants Sri Lankan Regime To Midwife a “Tamil Kurdistan “ To Serve As Permanent Proxy. | dbsjeyaraj.com
Sri Lanka received very minimal of US or Israeli weapons during the fourth Eelam war. The majority of the arms came from China and Pakistan.
Singapore don't need to meddle with the super powers because Singapore is located in a relatively calm location both politically and geographically. Singapore's fate would've being completely different if it was located near China just like Hong Kong, Taiwan or the Korea. AFA Sri Lanka is concerned, it is unavoidable that Sri Lanka is drawn into the battle between India and China. Their is no other option left to us other than siding with one faction. That is the choice our politicians should make when they come to power. MR sided with China and Ranil sided with India.
Further more Singapore didn't need to develop any ties with the West where the tie was already made secure by the British. British had made Singapore to be a leading port facility before they left it to the locals. Lee Kwan Yew only had to continue what Brits have left up. Also Malaysia didn't have an issue which US has taken interest into.