Quick side notes:
Many departments in CT, especially when NECS was a major vendor - had encryption available to them, but was not widely used. DVP-XL was the common algo used, but like most analog encryption the voice quaility wasn't the greatest - the CPU's in the radio and board hardware was the best possible. It had to do A/D conversions and other associated tasks.
Now on digital systems, the A/D is already done and the boards (or software) just applies the math so the voice quaility is the same.
FDNY tried P25 on one of the TAC channels many moons ago with their XTS3500's, and it wasn't a digital issue but ended up a programming issue based on what they were trying to accomplish at the time. This issue is what helped to develop the FDNY specified programming and the TPS options in the current radios. Essentially they get P25 radio ID sets with analog voice, among others.
The City attempted to sue Motorola claiming that the radios were prototypes but the XTS3500 is an updated version of the 3000 with a faster CPU and allowed for stronger encryption to meet some .gov customers. When the FDNY bought the 3500's the 5000's were already in prototype testing.
Prior to that, FDNY used Sabers and had been the workhorse of NYC for a very long time. In fact Motorola developed a short lived SSE5000 for NYPD so that they could reuse all their accessories. The radio was awesome, but was never developed further as Motorola was cutting costs and wanted to be moved out of the specialty radios niche as profit margins were slim. The XTS4000 was also killed around that time. You can't make a decent profit with many various tooling for a couple of customers.
FDNY didn't use the older digital option by Motorola (VSELP) - which was introduced in late 1994 early 1995 with the ASTRO Digital Saber. VSELP was only offered in the ASTRO Saber and ASTRO Spectra. LAPD was a major customer of the VSELP option but wasn't implemented. This was the only model and customer in which MODAT was available - and then went away, why....
...because in 1996 APCO settled on DVSI's IMBE CODEC for a digital standard for public safety. LAPD then updated their radios to IMBE. In 1996 Motorola released firmware and software to support IMBE.
In 1996 Motorola also released the XTS3000. As a note when CSP was building out the Smartzone system, ASTRO Sabers were bought and used during testing and initial use but the state went to the XTS3000 fleetwide due to its potentional longivity of a newer product.
So back to CT, when the Spectra was rolled out, a bunch of things happened. Many departments were in the process of replacing 1960's-1970's era radio systems and Motorola (and GE) was marketing a whole new generation of products aggressively. NECS had a very effective sales team and Motorola also still had its sales and marketing teams.
You saw many departments upgrade to the Centracom II console system with DVP-XL encryption option on the main or secondary police channel, MSF5000 repeaters, Spectra mobiles, MT1000 portables and typically Sabers with encryption for supervisors.
You renewed your fleet in many cost saving ways while taking a big leap in technology. SNET at the time had really good pricing on leased lines for public safety so as the radios were upgraded, remote receive sites and sometimes additional transmitter sites where installed.
So fast forward to the release of P25 and encryption, you saw more widespread use of encryption when grants were flowing, costs were lower and quaility improved. It's nothing, just easier to implement.
So see, mostly on topic with some corrections to other posts.