why E2C exist only on coinbas and not on any other platforms ?
Because e2c is is a scam and a team of scammers have done it. All these scammers are Iranians and since 2015 they have run several different scams such as Adrows, Unifunds, Worldwide, and e2c and v2c.
All of these are Ponzi schemes and are based on referral programs namely pyramid schemes. These scammers do pyramid schemes and all the scams I said above are pyramids. Do not invest in those scams and do not lose your money, these scammers are doing these things for several years now and all they do is stealing money and lying and pretending that everything is fine but the reality is that they design websites and pretend the website belongs to a company! which is a lie and all they do is pyramid schemes and referral programs by promising people high returns which is totally illegal.