They're mostly not manufactured in Singapore. They're designed in Singapore (formerly the UK), manufactured mostly in Malaysia and the Philipines (where labour is cheaper, [1]) and I presume the shift is entirely for tax reasons – in contrast to the UK it has far lower corporate taxation rates, and relevantly for Dyson himself, no capital gains tax at all [2] unlike the UK, which I presume will dramatically improve his income. The fact that they'll be in / closer to the same timezone as the manufacturing base probably helps as well.
[1] https://www.quora.com/Where-and-how-are-Dyson-vacuums-made?s... [2] https://ebos-sg.com/singapore-is-a-tax-haven/