outside of trivial transfer transactions there are much more complicated things you can do with smart contracts such as decentralized lending and decentralized exchange of assets
these are more like arbitrary atomic changes to on chain state that can affect many wallets and different contracts (and depend on the existing state) rather than just a transfer from my wallet to another address, which can be reordered freely
see protocols such as uniswap, compound, aave, synthetix, sushiswap, liquity, etc.
these are transactions with extremely high value and often extremely urgent and not possible to merge together - e.g. the both liquidate the same unhealthy loan position (could be worth ~$10m+)
the whole point is it's not remotely easy to just "reconcile separately" when you have two mutually exclusive financial operations - these are not code changes made by mutually cooperating developers happy to change their code to resolve merge conflicts, they are actively fighting against each other
edit: this also point out how having a centralized entity decide the ordering of transactions is a horrible idea - sequencing is worth enormous amounts of money and you could not be trusted to resolve transactions in a way that is sometimes against your interests but in the interest of other participants in the network
Settle positions between two mutually non cooperating parties. Your github solution doesn't consider that many non cooperating parties may want to do conflicting things on chain and you need a trustless way to resolve those conflicts. First writer wins to a centralized database at github is not an acceptable settlement method for billion dollar transactions.
EDIT: A blockchain is not just about keeping a history, it's also about maintaining liveness of the chain and preventing censorship even when many non cooperating parties are involved with conflicting incentives.
The time-value still comes into play in the form of eth transaction fee. If you're flash loaning to take advantage of an open arbitrage opportunity there will be other parties trying to take advantage of it, so you will pay more to get your transaction in before theirs.
For a lot of transactions like this its actually miners who can detect and rewrite these transactions to take advantage of the arbitrage opportunities first, for this reason this cost is called "miner extractable value" or MEV.
However, note this fee doesn't accrue to the lender!
these are more like arbitrary atomic changes to on chain state that can affect many wallets and different contracts (and depend on the existing state) rather than just a transfer from my wallet to another address, which can be reordered freely
see protocols such as uniswap, compound, aave, synthetix, sushiswap, liquity, etc.