Every custom rifle builder has to, at some point, build a rifle on an Enfield. This is primarily to see if he can make it not look like an Enfield! They were popular for big cartridges because the action is kind of large and makes a good large rifle.
The P14 is often recommended for conversion to a magnum. The reason given is that the bolt face doesn't have to be opened up. This is a sure sign the advisor has never built a rifle since opening up the bolt face is not a big deal. Opening up the magazine and receiver is a big deal.
There are some advantages to the P14/M17 actions for serious rifle purposes. Many prefer the #### on closing system for rapid fire. The angled locking lug seats help to force a tight cartridge into the chamber. On extraction, as soon as the bolt moves, it is loose. The negative features amount to one; the ejector spring. There are two kinds; those which have broken and those which have not broken yet!
They are not really the ideal for big cartridges but obviously, they can be used for big cartridges and many like using them for this purpose. They need a lot of opening up but there is plenty of iron to work with.
By the way, in the picture with the two rifles (the lower one being a fullstock) I don't think that top rifle is an Enfield. I think it's a pre-64 Model 70. Regards, Bill.