The reason the marketing you’re seeing is about affordability and ease of degree attainment is that generally, that’s what people who want to complete online degrees are looking for. They’re looking for a relatively low-cost way to get a credential they need without it interfering in their daily life and career too much.
There are two issues I see here.
- Generally (very generally) speaking, online master's programs are not good preparation for doctoral programs. This is especially true for someone trying to switch fields, particularly in the humanities. Graduate-level humanities course are often largely discussion-based and depend upon a cohort of students coming together to dissect the material. Doctoral programs will also require letters of recommendation, but online programs make it difficult to develop the kinds of relationships you need with your graduate professors to get strong letters. That's probably why you're not seeing very many English MA programs that are conducted entirely online.
- You said that you work at a biological research company. Was your undergraduate degree in English or a closely related field? If not, there may be some prerequisite coursework you'll be expected to complete before you are competitive for an English PhD program.
Frankly, preparing for applications to PhD programs (including potentially getting an MA) requires a sacrifice of time and money. I’m not saying that you should live in poverty while you pursue, but it may be necessary (for example) to curtail your travel for a period of time while you complete the MA program. Is it possible for you to complete the MA at the University of Cincinnati part-time?
With all of those things said, there ARE online master’s programs in English. I can’t testify to their strength, but here are some:
Arizona State University (https://asuonline.asu.edu/online-degree-programs/graduate/master-arts-english)
Southern New Hampshire University
Bowling Green State University (https://www.bgsu.edu/arts-and-sciences/english/graduate-programs/ma-english-online.html), where you will benefit from in-state rates I presume
Texas Tech University (https://www.depts.ttu.edu/english/grad_degrees/MA_in_Literature.php)
Morehead State University (https://www.moreheadstate.edu/study/MA-English/)
Northern Arizona University (https://ec.nau.edu/MastersDegrees/English-Literature-254/)
University of New Orleans (http://www.uno.edu/cola/english/graduate/online-ma-in-english.aspx)