The reason you did not get upgrade could be due to one of the following reasons:

1>, Your expense in the hotel is billed to your company rather than yourself
2>, Your rate is now a deep discounted corporate rate that upgrade may be excluded from such rate
or/and
3>, You are treated as a long stay guest and in many cases upgrade is excluded from such circumstances

A good hotel will try their best to please you in other forms. For example, you may receive odd fruit platter or drinks from the management once your stay is totalled exceeding certain number of nights. But do not expect upgrade. The policy on upgrade is not on how many night you stay, but on what rate you stay. If you are locked into one of the LOCALLY NEGOTIATED rate, IHG benefits will not apply in some cases.