Keyword Analysis & Research: why can't i merge and center in excel table

Keyword Analysis

Keyword	CPC	PCC	Volume	Score	Length of keyword
why can't i merge and center in excel table	1.11	0.6	926	42	43
why	1.32	0.2	9827	42	3
can't	1.67	0.6	1107	59	5
i	1.71	0.9	5390	81	1
merge	1.11	0.1	7334	12	5
and	0.51	0.3	5694	98	3
center	1.04	0.4	86	76	6
in	1.26	0.9	2994	78	2
excel	0.89	0.9	986	75	5
table	1.46	0.6	7190	35	5

Keyword	CPC	PCC	Volume	Score
why can't i merge and center in excel table	0.19	0.6	5689	44