Contact ESD protection vs Air gap ESD protection
Periphery or I/O connector ESD protection is indeed ineffective against ESD events in the middle of a board.
That is why ESD sensitive circuitry is typically enclosed in a housing.
And why it is recommended that repair, maintenance, or development work on such a device occur only in an ESD-protected work environment.
Many modern ESD-sensitive semiconductors include protection at the level of individually I/O pins, but for particularly sensitive circuits, or those where there's a fear that ESD might degrade performance without creating an immediately recognizable failure (eg, high performance RF/microwave parts), then those precautions would hold at least for production (vs possibly, development) examples.