Nobody can push an update onto Bitcoin. Each node runs the software its operator chose to install. A change only takes effect if enough of the network chooses to run it.
The usual path
- An idea is written up as a BIP, a Bitcoin Improvement Proposal, and discussed in public.
- Developers review it, sometimes for years, and implement it in software such as Bitcoin Core.
- Users and businesses decide whether to run the new version.
- For a soft fork, miners usually signal readiness, then it activates at a set block.
Economic weight
The nodes that matter most are those of people who receive payments: exchanges, merchants, wallets, individuals. They decide which coins they accept. A chain with different rules that they do not accept is simply another coin.
Developers write code but cannot force anyone to run it. Miners have hashrate but must mine coins people accept. Users have the final word because they choose the software that checks what they receive.