How come all the new subway lines in NYC are being done so slow?

I thought the US was a wealthy country, how come a simple subway extension is taking over a decade to finish? <br><br>The 7 subway extension took from 2007-2015, the 2nd Avenue subway took 10 years from 2017-2017 to add 3 stations, and the current 2nd Avenue subway extension is supposed to be built by 2035, but most likely 2040s.<br><br>Even countries like Vietnam & Egypt are able to create entire new subway systems in less time than it takes NYC to add 4 new stations.