I think there is a reason that yeshivas are designated for study of specifically Jewish texts. There are many things, including science, that can expand our appreciation of Hashem but aren't taught in yeshivot. Furthermore, a yeshiva is not supposed to be a place whereby all life skills are acquired e.g. learning a skill for earning a living, which is also crucially important.
Another reason is that most Rabbanim are not experts in the sciences so it seems inappropriate to ask yeshivas to teach/encourage study in this area specifically. In depth study in science is something that can be acquired in university and personal study. Yeshivot encourage dialectic learning in chavruta, this kind of learning is unique to yeshivas and often gets increasingly difficult when one leaves yeshiva - so utilizing this time for study of Jewish texts in chavruta is a prominent method of study.
What is a shame, from my experience, is that many Rabbanim don't have a basic understanding of science and relevant sources in Jewish literature to discuss the interaction between Torah and Science. Meaning, that once a yeshiva student leaves the yeshiva environment and may study science, the Rabbanim that he relied on previously don't necessarily know how to answer the questions that he may have, and rather than tackle them head on, they are involved in apologetics.
This is, in a sense, a cost benefit analysis; yeshivot would rather not teach outright science than talk about it in a mediocre non-expert manner, where they could run into problems.
why is this not encouraged in the yeshivas at all? the few yeshivas that study science...
You seem to be conflating encouraging study with incorporating the study in a curriculum. Consider clarifying what you are trying to ask.Considering the Rambam recommends observing nature to see the divine wisdom therein and develop a love of God, if so, why is this not encouraged in the yeshivas with this outlook?
In yeshivot with which outlook? The approach that science should be studied? Presumably those do study science, by definition. Those with the outlook that one should love God? Which Yeshiva would disagree? Consider editing to clarify what you are trying to ask.