Surely is a very strong statement here. I see no reason that a properly designed electronic timer wouldn't have effectively infinite lifetime, which is not possible with a practical mechanical timer. It has no moving parts (other than switches, which can be substituted for capacitive touch). A mechanical timer has many small mechanical parts and wear points, and can get gummed up over time if it doesn't outright stop functioning.

In practice, cost engineering is going to mean neither is completely reliable, but it should be cheaper to make an electronic timer reliable enough. Especially today, where the cost of a functioning mechanical timer is probably an order of magnitude more than an equivalent electronic timer.

I'm willing to believe that the best electronic switches can last longer than the best mechanical switches, but there's so many more ways for an electronic switch to fail that it's a lot easier for me to trust an off-the-shelf mechanical switch than an off-the-shelf electronic one, especially if the cost of failure of the mechanical switch is just an easy swap in of another one.

In what ways can a purely electronic, no moving parts, switch fail?

There are so many different mechanical things that can break, jam, get gummed up...

Capacitors can die, for example. Anything with a battery backup, the battery can leak and damage components. Electronics are more prone to ESD and water damage than mechanical parts.

Going into the realm of unlikely scenarios, electronics are more susceptible to EMPs.

The thing is: It is moving as there are vibrations. There is a fair amount of acceleration and a high frequency. Then there are temperature cycles as the machinery is not perfectly isolated. There is migration of atoms at contact boundaries. Plenty things move.