These centralized services just happen to be the current iteration. There will be others. It's hard to do make decentralized software well and up to now hasn't been the main thing so we have centralized software.

Before TCP/IP there were many competing networking 'standards' put out by various vendors, some were local nets but others also did routing, but TCP/IP has superceded them and many application protocols are created just for the purpose of interoperability and decentralization.