A number of reasons to stay at GSK range from comfort level in their current position, gaining experience to bridge to another pharmaceutical company or not to far from retirement of 5 years or less.
It does seem dysfunctional here but many pharma companies are dysfunctional in one way or another.
If GSK had a strong portfolio and pipeline, other than a vaccine or two, morale would float upwards.
Things won't change here which is a reflection of it's market price over the past 15 years.
If you don't enjoy your work here take a risk and leave.