NPA
 

Why adding 50 feet in an non-precision approach would prevent descending below MDA in case of GA? I mean in a NPA we would descend to MDA then level off until our MAP then initiate a go-around, which means we wouldn't go below MDA.

NPA
 

Because in EASA-OPS levelling off at the MDA is not allowed. Only CDFA. (There are exceptions though).

Yes, NPA under EASA-OPS have DA rather MDA, so it is a CDFA and does require the 50 feet addition, but what about non EASA-OPS charts where MDA and MAP are published, do we add 50'?

Ive yet flown an approach in EU land that has a DA. My outfit adds 50' to the MDA. This now makes it a DA for CDA approaches.

The 50' increment caters for the 30' loss during a Go around which helps comply with the 'do not go below MDA' rule.

Every NPA flown in CDFA technique is flown to a DA/DH if operating to EU/EASA OPS.

According to AMC1 CAT.OP.MPA.115 the following applies:

(4) The required descent path should be flown to the DA/H, observing any
stepdown crossing altitudes if applicable.

(5) This DA/H should take into account any add-on to the published minima as
identified by the operator’s management system and should be specified in
the OM (aerodrome operating minima).

Therefore the minima in the route manual, which is usually OM-C, should include those add-ons if they are required. For us the normal LIDO minima are that, and haven't changed in most cases when we switched from MDA to DA.

My LIDO plates only state MDA not DA so we include the 50'.

My bold above; this is the root of the issue. Under EASA rules, everything is down to the operator.
If the operator has surveyed every NPA at every arport they operate to or use as an alternate and determined that the obstacles that limit the MDA are not in the area where dipping below during the first stage of a GA would be an issue, then they can use the MDA as a DA. They can even do it on an individual approach basis if they wish, as long as there is a sensible way of publishing what to use for each one, e.g. customised approach plates.
However, only the largest operators have the resources to do this, or even the desire. So the majority just say "add 50ft".
Let's face it, how many times is it actually going to make a difference to whether you get in or not. And if you don't, it's not a safety issue since you still have fuel to divert and land at your alternate with more than final reserve (you do, don't you???).