STA and CTS do not have the same goals. As the names suggest - STA is a timing 'Analysis' step, where we do an analysis using tools such as Primetime to check if the design meets the timing specification. CTS on the other hand is a clock tree 'Synthesis' step - it is a step in the Implementation process of the chip, where the clock tree(s) is inserted into the design to connect a clock(s) to all FF in the design. Unlike regular logic, the clock is a high fanout net and needs special treatment to ensure that it reaches all the FF with minimal skew, latency etc. Hence this is done as a separate synthesis step after regular logic synthesis. Once the clock tree has been inserted, we do what is called a postlayout STA to check if all timing can be met.
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