The usual patterns that crop up are:

1) Lack of institutional knowledge. No one even knows how to get started and bringing in foreign expertise may be prohibitively expensive.

2) Economics don’t pencil out even in higher income countries compared to BRT systems, especially because high density and heavy traffic means the lines usually have to be grade-separated which adds additional costs compared to an at-grade system.

3) Corruption makes development impossible. No well-established processes for expropriation exist, or the country is given over to clientelism such that landlords won’t give up what they own and hamper the development process via political connections.

BRT is usually the most effective solution in places where grade-separated rail is not yet viable as it allows a right-of-way network to be established that can later be upgraded to rail. This doesn’t solve problem 3, which requires a comparatively authoritarian approach to overcome the incentive problems at play; this is why the Chinese have generally excelled in the space over the last 20 years.

The water table surely has something to do with it, but they could put much of it above ground like Bangkok does (erm, Bangkok should be listed as doing ok, even if they aren't doing as well as Singapore).

China built A LOT in the last 15 years. Beijing before 2008 had line 1, 2, a couple of suburban lines (13 and another one out east), and that was it. I don't think any other country has ever built infrastructure so quickly, so it isn't really fair to compare them to China.

Or electric bikes and cars

Democratic governments are weak on deficit spending, especially poor ones, the debt from their tiny stretch of high speed rail almost became a scandal.

Probably a combination of overall wealth and government policies/stability/priorities. I'd probably add Hong Kong to the list of cities with pretty good public transit but, overall, it's pretty bad in that area of the world relative to cities that you'd generally consider to be "good."

Bangkok has built a lot of transit in the past decade, 6 lines on top of an already-substantial existing network. Still plenty of projects under construction as well. This alone puts it way ahead of Jakarta in terms of quality of life IMO.

KL has subways. Even better is the KL city bus network which is free, air conditioned, and has free wifi. Despite Malaysia being a nominally muslim state, I found it multicultural and tolerant. If it wasn't for the heat and humidity, I'd consider it a great place to retire.

> I am not sure why SE Asian cities aren't going as all in on mass transit like China

Eminent domain and mass demolitions were very common in 1990s-2010s China, and to a degree that I have not seen in other authoritarian and nominally communist states like Vietnam or even Laos, let alone other less authoritarian states.

Entire neighborhoods, villages, and towns were razed to build the urban areas that make up China today.

Beijing [0][1], Shanghai [2][3], and other cities across China [4] all saw massive urban demolitions until the Central Government banned them in 2021 during the Evergrande crisis [5] due to limited utility and rising urban discontent.

Back in the day, it was somewhat common to see news about some random Jie commiting a terrorist act in retaliation for being evicted from their homes [6][7] due to this urban demolition program, and partially helped Xi consolidate power as most officials affiliated with these programs were deeply corrupt, and were often felled during the anti-corruption purges (ironically, Xi oversaw similar initiatives in Zhejiang in the 2000s).

Most other governments don't see the utility of implementing a similar style of program.

[0] - https://www.smartcitiesdive.com/ex/sustainablecitiescollecti...

[1] - https://www.theguardian.com/world/2007/jun/06/sport.china

[2] - https://web.archive.org/web/20130324195541/http://www.unhabi...

[3] - https://archive.nytimes.com/sinosphere.blogs.nytimes.com/201...

[4] - https://www.sixthtone.com/news/1002775

[5] - https://english.www.gov.cn/statecouncil/ministries/202108/31...

[6] - https://www.bbc.com/news/world-asia-china-18018827.amp

[7] - https://www.nbcnews.com/id/wbna34450213