Why does At&t still have crap routers/outdated equipment compared to all other ISP's?????

This past year bought a new house in a new construction area of FL and At&t was the only one to pre-install fiber internet services in the neighborhood so was forced to use them until another provider does an install. Running 1gb fiber unlimited data with arris BGW210-700, had the U-verse model prior to this one due to constant wifi issues that kept popping up. Point is Att is one of the very few major ISP's who are still providing outdated Modem/routers and do not allow you to use a certified modem/router for better home networking. i run a media server and a netgear 5gbE switch, plus several other devices that take up a large amount of bandwidth and due to having a crap router without even Link aggregation, causing me to bottleneck my home network with subpar lan connection to the modem and crap wifi capabilities. Question being why is Att so far behind the power curve when it comes to in-home equipment???? And yes i would do a pasthough and use another modem but my 400$ Netgear Nighthawk XS4 is a cable modem with no ethernet port for internet connection; so i'm not spending another 3 to 400$ just to use passthrough on a company that refuse to offer better equipment options, one of the major areas Att is failing at. once comcast gets there service in, in the next couple months i may be switching over due to Att's lack of keeping up with current technology in home, costing me time and way too much frustration.