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I am looking to produce 50kW for an off grid solar project. Ideally, I'd like to have a high voltage DC battery system with a high power battery inverter and charge controller.

I have only found a couple high VDC (384V) inverters and charge controllers, and they are from Chinese manufacturers. I'm a little hesitant to buy from them.

All of the big companies only use 12, 24, and 48 VDC. I understand that it's the most common and you don't need much power for a home, but if I want to produce 50kW at 48 VDC that's over 1000A! If I run that in parallel to 48V inverters I would need 10 or more inverters. That is a lot of wire and work.

Is there an electrical reason why they would cap these products at 48 VDC?

60VDC is the cut-off for Safety Extra Low Voltage, or SELV, as spelled out in UL 60950-1. Besides being lower voltage, SELV circuits are also isolated from the mains by reiniforced insulation, which has specific spacing and materials requirements.

48V falls below this SELV threshold with some margin.

Wiring for voltages above this SELV level is considered in the same class as line voltage, and typically requires an electrician to install.

More here: https://www.edn.com/electronics-blogs/power-supply-notes/4414411/What-does-SELV-mean-for-power-supplies

Field-assembled battery hardware can't go outside of SELV without help

The primary limitation on the DC bus voltage of most off-grid systems is indeed due to touch safety limits (60VDC/42.4VAC SELV limit), but that's not due to who's installing it. Instead, the issue is parts availability: lead-acid single cells and monoblocs of the sizes used in off-grid systems generally are not available with touch-safe terminals due to manufacturability and application diversity issues. This can be somewhat overcome, depending on the environment, by using a battery cabinet or battery room as the touch safety boundary, or by using a factory-assembled and listed energy storage system, but that leads us to our next issue.

DC switchgear is hard

Light-duty LV AC mains switchgear (MCBs and associated mounting/bussing systems, as well as fusible switches/disconnectors, garden-variety mains fuses, and so forth) is, of course, readily available for typical utilization voltages. However, only a limited subset of this gear is rated for DC service at all, and if so, its ratings will be limited to around 48-60VDC. Furthermore, disconnectors and such intended for solar service, while rated for high voltages, have very low short-circuit/interrupting ratings in the grand scheme of things. This is because solar panels are inherently current limited sources: no matter how long your string is, it won't put out much more than its rated Isc no matter what you do to it, and solar panel Isc values are on the order of amps, not kiloamps.

This means that you need much heavier-duty switchgear for DC service at mains-voltage-equivalent DC voltages, as battery strings are capable of kiloamp-class fault currents (easily equivalent to a mains source in this regard), and DC arcs are indefinitely self-sustaining once struck vs. AC arcs which will self-quench at zero crossings. Furthermore, even heavier-duty gear such as DC rated industrial-type MCCBs and heavy-duty fusible switches is often limited to 125VDC for single pole breakers and 250VDC for all-pole switching in multiple pole devices. While there are a few fusible switches out there that have ratings up to 600VDC, these are also limited by the inability to get fuses rated for mains OCPD service at voltages above 300VDC with only a few exceptions.

Interrupting ratings are another issue; achieving DC system short-circuit ratings over 10kA requires careful component selection, and even the most robust breaker and fuse designs available only achieve 100kA or less of DC interrupting rating.