Electronic – Why are the components unconnected in the middle of the breadboard

Here's a picture of a board which had some headers forced into it which were too large, damaging the contacts:

The outer rows of the Sharpie'd area make intermittent contact, so we avoid the whole section. Notice that some of the numbers are rubbed off, and also notice the burnt spot at the top of the picture where something burned up.

The breadboard still has two other middle sections, and this section is only 20 rows tall, so that leaves 172 good rows. On a university budget, that doesn't merit replacing the board. If you are demonstrating breadboarded circuits to a client, you should probably replace the whole thing.

By the way, this board is at least 8 years old, and still works fine except for the indicated area. I've only been around it for three years, but no one has had any problems with it that I've heard of.

Best bet is usually some DIY if you have not got too many.

Use 200 mil centre sockets if available or socket strips,

or cut a socket in two and solder two strips onto a piece of veroboard/vector board/whatever you call board with copper strips with holes in it.

Solder socket to board and solder a row of pins through board outside socket so they have (probably) 400 centres which will allow plugging into a standard breadboard.

Something like below but with your two rows of socket pins in the centre and with pins to breadboard bottom soldered

You can buy pins suited to this - and I have used plated brass dressmakers pins in days of yore. The plated brass pins have about 3 million% better solderability than non-brass pins that I have tried, even though the brass is under the plating.