A lot depends on the query as to why. Remember, APF's can be of any size - and can be of the table or index leaf pages. But let's take a query like:
select * from table order by <pkey>
where <pkey> is some list of columns that is in a clustered index. In APL, the table is essentially the clustered index and as a result, ASE can do table scan with pure APF's (and even large I/O's) to perform the query. With DOL, it likely will have do an index leaf scan and a resulting datapage lookup for each leaf - which, of course, can take a lot longer. The index leaf scan can use APFs' - but the data page lookups might not.
It would be better to post the query and the output of the typical qp diagnostics such as:
set showplan on
set switch on 3604
set statistics io, time, resource, plancost on
set show_lio_costing on
set nodata on
set statement_cache off
go
<query>
go
set showplan off
set switch off 3604
set statistics io, time, resource, plancost off
set show_lio_costing off
go