Just to add on what Lehnsherr said, the current scarcity of IPV4 is a known issue and an urgent one, which is why a lot of major players are already moving to IPV6.
To put things in perspective, if we were to just run a whois and compare the range owned by Starhub (203.116.0.0/15, 203.118.0.0/18 which translate to 147,456 ip) and the range owned by MR (which is a few /24, probably less than a thousand addresses), it is easy to understand why Starhub has the luxury to give all their subscriber a public IP. Starhub public address pool is easily 100 fold more.
And I really do not think it is the case of MR short-changing the customer since it is highly possible that there is really no decent range of public IP belonging to the APAC region to purchase anymore or at a reasonable price.
I paid $50 for a MR public IP and i paid it happily.
I paid my $50 happily too. My point is the addresses are not exhausted; you've put it correctly: they're scarce, and therefore expensive. MR is not unique in not offering public IPV4 addresses - plenty of ISPs around the world do this. Carrier-grade NAT is well established. However, in the Singapore context, they're perhaps the only consumer ISP to not offer public IPV4 addresses by default.