Based on the Yahoo financial info, it looks like almost 100% of REGN stock is either owned by employees or institutions. If they do not split the stock it looks like they really do not want the public involved except in ETFs or mutual funds. If all the posters are actual owners then we are a rare breed.
Generally speaking, many investors are scared to death of owning a $280 stock and would not touch this with a ten foot pole. Doing a 5 or 6 to one split would put this in an area where the average Joe might make an investment. I know that value wise it does not matter whether you have 1 share at $280 or 6 shares at $46.67, which is what all the anti split folks throw up; however, having a $27 billion company with less than 100 million shares is a rarity.
I also own CL which will be splitting 2 for 1 on 5/15. The reason they gave was to allow more individuals to invest in their company. Even though value is based on earnings and growth and not absolute price, there are many who are just scared of owning these high price per share companies.