OK, I'll have a stab at this as I am an Orthodox Jew who keeps strictly kosher. Please keep in mind I can only speak for myself here though. And I haven't read the whole thread.
The Torah the Old Testament as Christians would call it sets out a series of dietary rules which set out which animals Jews can and cannot eat, and some various other rules. Over the years there have been many attempts to explain the rationale or 'system' behind the restrictions. Various explanations have included health, spirituality (eg we don't eat birds of prey), instilling self-control into us, instilling thoughtfulness about what we it, and lots of other explanations that you can google. The truth is that keeping kosher is one of the few commandments that we simply do not understand the rationale of.
So we do I keep it?
Because it has been part of my tradition for thousands of years. I love being a religious Jew, I love our heritage and traditions, and it's part of the package.
Others keep it because they have been told to -- even if they don't understand it. Please understand that I am not talking about brainless automatons here, I'm talking about people who have thought long and hard about why they want to be observant of the laws in the Torah (as in today's world, most people have a choice), and this is something they accept as part of their wider relationship with G-d. Hope that makes sense.
Yet others genuinely believe one/some of the various explanations that have been offered through the ages health, spirituality etc. These are not 'excuses', they are part of the way the religion has come to understand itself over millenia and are very real to people. Certainly I believe that kashrut (kosher) does have a spiritual dimension a lot of our lives is conducted over food and the way we prepare it and it is inseparable from the experience of Orthodox Judaism.
On a personal level, I have kept kosher all my life and so it has never been a problem. I have never in my life been tempted by pork or any other non-kosher item and would never give up my rich religious and cultural life for a piece of meat. Yes, I do sometimes wonder what various non-kosher foods taste like but I'm hardly starving! I don't really care if I never taste them.
The only problem I've ever had with keeping kosher is at work going out for meals with colleagues etc., they often feel awkward when I don't eat. Again, the truth is that I really genuinely don't mind being 'left out' of the meal I'm happy to tag along and sip at my diet coke (and eat my own food later), it's just that others are often uncomfortable. I have to say though that wherever I work, people have always been wonderful - taking me out on occasion to kosher restaurants, ordering in kosher meals and generally going the extra mile for me. It's a testament to the real multiculturalism in this country and the good nature of the British people.
There you go, hope that helps.