Alright so you wish to ask a philosophical question, namely "Why has the universe existed for so long?" but it seems you are speaking in terms of a scientific problem. First, you must realize, no matter what, when you ask an ill-defined question, you will get an ill-defined answer. Physically, it could be explained or "answered" by speaking of the Big-Bang theory, and the laws of thermodynamics. Somebody more well-read on Big Bang theory may be able to come in here with more detail, but I would say that after the initial "expansion" the law of energy conservation would be violated if were the universe just to stop its expansion contract and disappear. All of this, of course, must be taken speculatively because that is what it is.
If you're asking the philosophical question, then first realize that what you are asking is very similar to "Why is there something rather than nothing?", but also you must realize that if you are to ask your question philosophically, you must look at "What type of question is a "why" question" "What type of explanation does that entail and what type of explanation do I want?" You must also look at the terms of your question. I am not necessarily saying that you need to apply actual philosophical analysis ala Russel or analytic philosophy, but you must understand what you trying to ask. So, we already saw how the "Why" part of your question must be looked at, then there is "so long" which implies time, but what is time? And in what framework do you seek an answer? Concrete time, that is time as it is experienced and how that shapes our existence or "objective" time? "Objective" time being a measured construction, we cannot have "objective" without measurement and "so long" is a vague "time interval" and "long" being vague cannot be understood in terms of an "interval" of time unless it is arbitraily stated that "t>x is long". But it seems as though you are seeking a fundamental or ontological answer, and in that case, the question of what is entirely independent of humans and the measurable "objective" frameworks we use to create an indpendant structural picture cannot even be apprehended.
We do not know the meaning or relevance of time independent of us, and then if by "so long" you are simply referring to structure and how so much structure has continued to "evolve", that is, develop in complexity, then you find that you aren't asking a philosophical question, but a speculaitve question from the perspective of science and how to scientifically search for the answer, but then you must accept a scientific answer.
Oh yea, going back "If philosophy is not physical what is it?" That presupposes a philosophy, namely materialism and reductionism, and clearly shows that you are not attempting to philosophize but to speculate
And like others said, don't confuse concepts such as "The evolution of the universe" or the "Devolopment of the universe and how certain structures and levels of complex interaction have emerged" with "Evolutionary theory" in terms of Biology. You said something about certain organisms not having "predators", true, but they do have "ecosystems" and biological evolution is inherently a a two-sided aspect, it is "Adapting" to its "environment" so the organism with no predator, must still "interact" with its environment in order to maintain homeostasis and continue to exist, it may not have another organism as a predator, but it still is not a closed independent thing, it is characterized, by its interaction. What would a universe "interact" with, what would the universe "adapt" to ?...And if this is your question, then your confusing the "framework" devised by us to understand nature, with nature itself and how all time-processes must be...I'm sorry if I'm attributing so many possible questions to your quesiton, but you must realize this is due to my (and most likely everyone elses, possibly yourself) misunderstanding of what the question is asking in the first place