Nodes, in the Bitcoin white paper sense, are miners. They a…

Nodes, in the Bitcoin white paper sense, are miners. They are not hobby relay boxes burning bandwidth for ideology. Miners are economically disciplined actors. They create blocks, accept transactions, validate competing blocks, and decide which chain to extend.
A miner is incentivised to link because isolation is expensive.
Let:
R = block reward + transaction fees
p = probability of finding the next valid block
s = probability the block becomes stale/orphaned
L = propagation latency
C = connectivity cost
Expected return is roughly:
EV = pR(1 - s) - C
Now increase L. The miner hears about competing blocks later. The miner’s own blocks reach other miners later. The stale risk rises. So s rises, and EV falls.
That means direct, high-quality connectivity to other miners is not charity. It is not “flood fill.” It is profit protection.
A miner who refuses to connect well loses money. He may keep mining on stale information. He may build on a block already superseded. He may find a block and fail to propagate it fast enough. He may miss fee-bearing transactions. He may provide worse service to merchants and payment processors. All of that reduces revenue.
So miners rationally form links because the market punishes isolation.
This is also why non-mining relay nodes are not the source of security. A relay-only machine does not create blocks. It does not compete for revenue. It does not bear stale-block risk. It does not settle transactions. It is merely a communications accessory.
The network does not become robust because a “solo libre relay node” exists. The network becomes robust because miners have a direct economic incentive to connect, propagate, validate, and remain in sync with other miners.
Connectivity is not a gift. It is part of the mining business model.