How much would it cost to build?
How much would it cost to maintain?
Who is going to pay for it?
I dunno. Is it worth at least looking into? Space flight is quite expensive. A solution involving using mountains may still be cheaper. Or it may not. It’s worth a ROM* estimate to see if it’s worth bothering with.
*Rough Order of Magnitude
Never mind. The answer is here: https://www.forbes.com/sites/quora/2017/01/04/why-arent-rockets-launched-from-higher-altitudes/#a902f983221f