Probably because the price has run up to historical valuation highs. The market cap is $37.5 Billion and someone would have to at least offer 20% premium or $45 Billion. That is a lot to chew on and KMB already has 48% debt.
I was trying to find 1990's data but unsuccessful; however, I owned CL back then and still do and the PE if I remember got to the low 40's. Historically CL has done better than KMB but not that much. The PE's were high because growth was high due to low commodity prices. Commodity prices have been high since the late 1990's, but they appear to come down. Historically long term stock bull markets are the product of long term commodity bear markets. We may be about to have another turn in these two financial classes with stocks heading higher and commodities lower to flat. The stock indexes are only slightly higher than 2000 2001 time frame.