MTA new subway car route lines

Why doesn't MTA replace all of their aging fleet with the new cars. I have seen new cars on
2,4,5,6,9,L, and R lines. All other routes that I have seen have the old 62 series cars. Why won't MTA get new cars for all lines?

I dont know about 9 which has been elimated from the system or R but yeah most of them. Some of the equipment is still good and dont need to be replaced. For example the R62 and R68 are still fairly new show why change it. What line needs the new routes? What do you think?

because the MTA's response to most of their ways is, "IF IT AINT BROKE, DONT FIX IT". The R62s and R62As, the R68 and R68As are from the mid 1980s, and they are all in relatively good shape. The reason the R32 and R46 arent being replaced is because the R32s are in better shape than some of the newer stuff or stuff built AFTER the R32s. Example, R32s will outperform a R38, a R40 slant and a R42 anyday of the week. The R46s are slated to go for overhaul again i believe. Basically them replacing 20 year old cars, is like you as a consumer buyin a new car every 2 years. Why do that when ur current vehicle might need jus a tune up and brakes and stuff thats cheaper than buying a new car? Why buy new when there is nothing wrong with the old. They replaced the Redbirds because some were cracking and falling apart. Look at us in MTA METRO NORTH! as old as they are, we still run a few sets of M1s!

Is the door arrangement on the R142 different than the R62? Perhaps the curve at South Ferry and the gap filler lines up better with R62 than the R142.