Perhaps it's among the cheapest because it's subsidized as a public good?

EDIT: According to Wikipedia, it's heavily tiered and heavily subsidized, but also that it shouldn't be particularly helpful for mining, unless they're splitting it into a bunch of accounts to stay in one of the lower tiers:

Domestic consumer pricing per kWh used, subsidized

4.95 @ 1 to 200 kWh

7.59 @ 201 to 300 kWh

11.73 @ 301 to 600 kWh

12.41 @ 601 to 900 kWh

12.98 @ 901 kWh onwards

(exchange rate of 4.4 MYR to US$1 on 24 November 2016)