Smart locks add convenience and a set of failure modes that mechanical locks do not have. The retained keyhole is a response to those failure modes rather than a legacy detail.
Power is the first dependency
Battery-operated locks warn as charge falls, but cold weather reduces available capacity and can take a lock from a warning to unresponsive quickly.
A motor driving a bolt draws a substantial current briefly, so a battery that reports adequate charge at rest may fail under that load.
Emergency contacts on the exterior, allowing a portable battery to power the mechanism, address this without requiring the mechanical key.
Radio failure is more common than lock failure
Remote operation depends on a network connection, a hub and often a manufacturer's servers, and any of those can be unavailable.
Locks that operate over a short-range direct connection from a phone remain usable during an internet outage, while cloud-dependent designs may not.
This is why local operation is worth confirming before purchase, since the difference only becomes apparent during a failure.
Software updates can interrupt operation
Firmware updates apply to locks as to any connected device, and an interrupted update can leave a device in a state requiring reset or replacement.
Manufacturers schedule updates for quiet periods and require adequate battery charge, which reduces but does not remove the risk.
A lock is a device where a small probability of failure carries a large consequence, which shapes how conservatively these updates are handled.
The mechanism itself is the weaker point
An electronic lock is usually fitted to a standard mechanical body, so the physical security is determined by that body rather than by the electronics.
Adding electronics does not improve resistance to forced entry, and a poorly fitted lock is no stronger for being connected.
Attacks against a door commonly target the frame and strike plate, which no lock addresses regardless of how it is operated.
Access records change what a lock is for
The most useful property is often not remote unlocking but the record of who entered and when, and the ability to grant temporary access.
Time-limited codes for tradespeople and visitors remove the need to hand over keys that cannot be recalled.
That record is also personal data held by whoever operates the service, which is a consideration alongside the convenience it provides.
Locks that keep their history on the device rather than on a server offer the same practical benefit without creating an external record of household movement.