1) Grab treated drivers better than Uber - e.g. the Grab app displays the destination so drivers who don't want to go far out of their way or into congestion can reject fares (whereas Uber used to hide destinations and heavily penalise drivers who reject trips).
2) Prices went up immediately after Uber exited, even now Grab has moved to a floating arbitrary pricing rather than mileage/time x $X. So both companies were providing significant subsidies which were unlikely to be unsustainable. Also Uber had defined hot-spots and if drivers idles in those areas with their app open they would receive an hourly wage (topped up with fares that they get). Grab doesn't do this currently according to drivers I've spoken to, its another form of subsidy to get customers a car faster and snatch market share.
3) Related to (1) above, Grab played the politics better. They got the taxi drivers on-side (Grab was originally MyTeksi and just used to hail a licensed taxi) and also navigated govt legislation better vs Uber strategy of just ignoring/skirting laws and trying to force their way through with market share and popularity. I was in an uber a few years ago and the car was pulled over by airport police, I was told to get out and find another ride - wasn't clear if the driver was getting fined or a warning.
4) The super app is annoying garbage. Now I need 3 laggy clicks to book a car rather than one tap on the app. Everyone wants to be WeChat and is failing with bad software.
5) Malaysia's govt is cracking down with new regulations. E.g. from later this year all Grab drivers will need to register their cars as a public service vehicle. This has implications for insurance but since it is a public record will also cause devaluation of used vehicles that have been driven for Grab (since any potential buyer can look up this record and negotiate a better price - Malaysians don't like heavily used second-hand goods). A few drivers I have spoken to have said they will quit driving for Grab before the legislation comes in since they are only part-time and their estimated loss of car value out-weighs all the money they could earn driving grab a few nights a week. So this will pull supply out of the market.
6) Grab was earlier than uber in allowing cash payments which anecdotally I've heard users and drivers really like. One curious anomaly is that Grab is now also charging cancellation fees. But if you booked a car with cash payment and then cancel, then the next time you book a car the fee will be added onto your fare. And the driver has the responsibility to advise you and collect the fare. A driver was telling me he keeps getting 1 star reviews from riders who get angry at him adding on the late fee (which could have been from days earlier).