6500/7600 is weird beast where the same HW architecture (and well 4 generations of it that are to some extent compatible although internally very different) are used as both high port density ethernet switch (6500) and as an router (7600, the only meaningful difference in the HW is that 7600 is painted white). In almost all configurations all the forwarding decisions are done in hardware, which involves somewhat expensive memory chip that Cisco calls TCAM (Ternary Content Addressable Memory), essentially an SRAM array interspersed with comparators that can find a FIB record matching the destination address with most specific mask in one cycle. In the actual implementation it is not a full TCAM and involves some kind of hashing and lookup takes multiple cycles, to make it not ridiculously expensive, but still it is not priced like your typical off the shelf 6T-SRAM (which by itself is orders of magnitude more expensive than random high volume DDRx SDRAM).
Another thing is that the thing is somewhat old and designed by Cisco who will not go out of their way to produce something that makes it obvious that their product can be replaced by a x86 box running Linux And good luck making a x86 box that has 720Gbps bandwidth and 144 ethernet ports. There is a question of exactly what is the real world practical application for 48 port gigabit linecard (there even is a PoE option, 6500 in right config can prowide kilowatts of PoE) in a router that can speak BGP, but well, you can build such a thing from 6500.
Another thing is that the thing is somewhat old and designed by Cisco who will not go out of their way to produce something that makes it obvious that their product can be replaced by a x86 box running Linux And good luck making a x86 box that has 720Gbps bandwidth and 144 ethernet ports. There is a question of exactly what is the real world practical application for 48 port gigabit linecard (there even is a PoE option, 6500 in right config can prowide kilowatts of PoE) in a router that can speak BGP, but well, you can build such a thing from 6500.